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1.  Broca's Area Homologue in Chimpanzees (Pan troglodytes): Probabilistic Mapping, Asymmetry, and Comparison to Humans 
Cerebral Cortex (New York, NY)  2009;20(3):730-742.
Neural changes that occurred during human evolution to support language are poorly understood. As a basis of comparison to humans, we used design-based stereological methods to estimate volumes, total neuron numbers, and neuron densities in Brodmann's areas 44 and 45 in both cerebral hemispheres of 12 chimpanzees (Pan troglodytes), one of our species’ closest living relatives. We found that the degree of interindividual variation in the topographic location and quantitative cytoarchitecture of areas 44 and 45 in chimpanzees was comparable to that seen in humans from previous studies. However, in contrast to the documented asymmetries in humans, we did not find significant population-level hemispheric asymmetry for any measures of areas 44 and 45 in chimpanzees. Furthermore, there was no relationship between asymmetries of stereological data and magnetic resonance imaging–based measures of inferior frontal gyrus morphology or hand preference on 2 different behavioral tasks. These findings suggest that Broca's area in the left hemisphere expanded in relative size during human evolution, possibly as an adaptation for our species’ language abilities.
doi:10.1093/cercor/bhp138
PMCID: PMC2820707  PMID: 19620620
cytoarchitecture; evolution; great ape; handedness; stereology
2.  Planum Temporale Surface Area and Grey Matter Asymmetries in Chimpanzees (Pan troglodytes): The Effect of Handedness and Comparison with Findings in Humans 
Behavioural brain research  2009;208(2):436-443.
The planum temporale (PT) is the bank of tissue that lies posterior to Heschl’s gyrus and is considered a key brain region involved in language and speech in the human brain. In the human brain, both the surface area and grey matter volume of the PT is larger in the left compared to right hemisphere in approximately 2/3rds of individuals, particularly among right-handed individuals. Here we examined whether chimpanzees show asymmetries in the PT for grey matter volume and surface area in a sample of 103 chimpanzees from magnetic resonance images. The results indicated that, overall, the chimpanzees showed population-level leftward asymmetries for both surface area and grey matter volumes. Furthermore, chimpanzees that prefer to gesture with their right-handed had significantly greater leftward grey matter asymmetries compared to ambiguously- and left-handed apes. When compared to previously published data in humans, the direction and magnitude of PT grey matter asymmetries were similar between humans and apes; however, for the surface area measures, the human showed more pronounced leftward asymmetries. These results suggest that leftward asymmetries in the PT were present in the common ancestor of chimpanzees and humans.
doi:10.1016/j.bbr.2009.12.012
PMCID: PMC2831152  PMID: 20035802
chimpanzees; planum temporale; brain asymmetry; handedness; gestural communication
3.  Planum Temporale Grey Matter Asymmetries in Chimpanzees (Pan troglodytes), Vervet (Chlorocebus aethiops sabaeus), Rhesus (Macaca mulatta) and Bonnet (Macaca radiata) monkeys 
Neuropsychologia  2011;49(7):2004-2012.
Brain asymmetries, particularly asymmetries within regions associated with language, have been suggested as a key difference between humans and our nearest ancestors. These regions include the planum temporale (PT) - the bank of tissue that lies posterior to Heschl’s gyrus and encompasses Wernicke’s area, an important brain region involved in language and speech in the human brain. In the human brain, both the surface area and grey matter volume of the PT is larger in the left compared to right hemisphere, particularly among right-handed individuals. Here we compared the grey matter volume and asymmetry of the PT in chimpanzees and three other species of nonhuman primate in two Genera including vervet monkeys (Chlorocebus aethiops sabaeus), rhesus macaques (Macaca mulatta) and bonnet macaques (Macaca radiata). We show that the three monkey species do not show population-level asymmetries in this region whereas the chimpanzees do, suggesting that the evolutionary brain development that gave rise to PT asymmetry occurred after our split with the monkey species, but before our split with the chimpanzees.
doi:10.1016/j.neuropsychologia.2011.03.030
PMCID: PMC3151738  PMID: 21447349
nonhuman primates; planum temporale; brain asymmetry; laterality; language evolution
4.  Chimpanzee Vocal Signaling Points to a Multimodal Origin of Human Language 
PLoS ONE  2011;6(4):e18852.
The evolutionary origin of human language and its neurobiological foundations has long been the object of intense scientific debate. Although a number of theories have been proposed, one particularly contentious model suggests that human language evolved from a manual gestural communication system in a common ape-human ancestor. Consistent with a gestural origins theory are data indicating that chimpanzees intentionally and referentially communicate via manual gestures, and the production of manual gestures, in conjunction with vocalizations, activates the chimpanzee Broca’s area homologue – a region in the human brain that is critical for the planning and execution of language. However, it is not known if this activity observed in the chimpanzee Broca’s area is the result of the chimpanzees producing manual communicative gestures, communicative sounds, or both. This information is critical for evaluating the theory that human language evolved from a strictly manual gestural system. To this end, we used positron emission tomography (PET) to examine the neural metabolic activity in the chimpanzee brain. We collected PET data in 4 subjects, all of whom produced manual communicative gestures. However, 2 of these subjects also produced so-called attention-getting vocalizations directed towards a human experimenter. Interestingly, only the two subjects that produced these attention-getting sounds showed greater mean metabolic activity in the Broca’s area homologue as compared to a baseline scan. The two subjects that did not produce attention-getting sounds did not. These data contradict an exclusive “gestural origins” theory for they suggest that it is vocal signaling that selectively activates the Broca’s area homologue in chimpanzees. In other words, the activity observed in the Broca’s area homologue reflects the production of vocal signals by the chimpanzees, suggesting thast this critical human language region was involved in vocal signaling in the common ancestor of both modern humans and chimpanzees.
doi:10.1371/journal.pone.0018852
PMCID: PMC3080370  PMID: 21533079
5.  A Comparative Magnetic Resonance Imaging Study of the Anatomy, Variability, and Asymmetry of Broca's Area in the Human and Chimpanzee Brain 
The frontal operculum—classically considered to be Broca's area—has special significance and interest in clinical, cognitive, and comparative neuroscience given its role in spoken language and the long-held assumption that structural asymmetry of this region of cortex may be related to functional lateralization of human language. We performed a detailed morphological and morphometric analysis of this area of the brain in humans and chimpanzees using identical image acquisition parameters, image analysis techniques, and consistent anatomical boundaries in both species. We report great inter-individual variability of the sulcal contours defining the operculum in both species, particularly discontinuity of the inferior frontal sulcus in humans and bifurcation of the inferior precentral sulcus in chimpanzees. There was no evidence of population-based asymmetry of the frontal opercular gray matter in humans or chimpanzees. The diagonal sulcus was only identified in humans, and its presence was significantly (F = 12.782, p < 0.001) associated with total volume of the ipsilateral operculum. The findings presented here suggest that there is no population-based interhemispheric macroscopic asymmetry of Broca's area in humans or Broca's area homolog in chimpanzees. However, given that previous studies have reported asymmetry in the cytoarchitectonic fields considered to represent Broca's area—which is important given that cytoarchitectonic boundaries are more closely related to the regional functional properties of cortex relative to sulcal landmarks—it may be that the gross morphology of the frontal operculum is not a reliable indicator of Broca's area per se.
doi:10.1523/JNEUROSCI.2892-09.2009
PMCID: PMC2797078  PMID: 19923293
6.  Neuroanatomical asymmetries and handedness in chimpanzees (Pan troglodytes): a case for continuity in the evolution of hemispheric specialization 
Many historical and contemporary theorists have proposed that population-level behavioral and brain asymmetries are unique to humans and evolved as a consequence of human-specific adaptations such as language, tool manufacture and use, and bipedalism. Recent studies in nonhuman animals, notably primates, have begun to challenge this view. Here, I summarize comparative data on neuroanatomical asymmetries in the planum temporale (PT) and inferior frontal gyrus (IFG) of humans and chimpanzees, regions considered the morphological equivalents to Broca’s and Wernicke’s areas. I also review evidence of population-level handedness in captive and wild chimpanzees. When similar methods and landmarks are used to define the PT and IFG, humans and chimpanzees show similar patterns of asymmetry in both cortical regions, though humans show more pronounced directional biases. Similarly, there is good evidence that chimpanzees show population-level handedness, though, again, the expression of handedness is less robust compared to humans. These results stand in contrast to reported claims of significant differences in the distribution of handedness in humans and chimpanzees, and I discuss some possible explanations for the discrepancies in the neuroanatomical and behavioral data.
doi:10.1111/nyas.12109
PMCID: PMC3676728  PMID: 23647534
brain asymmetry; language; handedness
7.  Volumetric and Lateralized Differences in Selected Brain Regions of Chimpanzees (Pan troglodytes) and Bonobos (Pan paniscus) 
American journal of primatology  2009;71(12):988-997.
The two species of Pan, bonobos and common chimpanzees, have been reported to have different social organization, cognitive and linguistic abilities and motor skill, despite their close biological relationship. Here, we examined whether bonobos and chimpanzee differ in selected brain regions that may map to these different social and cognitive abilities. Eight chimpanzees and eight bonobos matched on age, sex and rearing experiences were magnetic resonance images scanned and volumetric measures were obtained for the whole brain, cerebellum, striatum, motor-hand area, hippocampus, inferior frontal gyrus and planum temporale. Chimpanzees had significantly larger cerebellum and borderline significantly larger hippocampus and putamen, after adjusting for brain size, compared with bonobos. Bonobos showed greater leftward asymmetries in the striatum and motor-hand area compared with chimpanzees. No significant differences in either the volume or lateralization for the so-called language homologs were found between species. The results suggest that the two species of Pan are quite similar neurologically, though some volumetric and lateralized differences may reflect inherent differences in social organization, cognition and motor skills.
doi:10.1002/ajp.20741
PMCID: PMC2804891  PMID: 19760676
brain evolution; bonobos; chimpanzees; laterality; cognition
8.  The Evolution of Brains from Early Mammals to Humans 
The large size and complex organization of the human brain makes it unique among primate brains. In particular, the neocortex constitutes about 80% of the brain, and this cortex is subdivided into a large number of functionally specialized regions, the cortical areas. Such a brain mediates accomplishments and abilities unmatched by any other species. How did such a brain evolve? Answers come from comparative studies of the brains of present-day mammals and other vertebrates in conjunction with information about brain sizes and shapes from the fossil record, studies of brain development, and principles derived from studies of scaling and optimal design. Early mammals were small, with small brains, an emphasis on olfaction, and little neocortex. Neocortex was transformed from the single layer of output pyramidal neurons of the dorsal cortex of earlier ancestors to the six layers of all present-day mammals. This small cap of neocortex was divided into 20–25 cortical areas, including primary and some of the secondary sensory areas that characterize neocortex in nearly all mammals today. Early placental mammals had a corpus callosum connecting the neocortex of the two hemispheres, a primary motor area, M1, and perhaps one or more premotor areas. One line of evolution, Euarchontoglires, led to present-day primates, tree shrews, flying lemurs, rodents and rabbits. Early primates evolved from small-brained, nocturnal, insect-eating mammals with an expanded region of temporal visual cortex. These early nocturnal primates were adapted to the fine branch niche of the tropical rainforest by having an even more expanded visual system that mediated visually guided reaching and grasping of insects, small vertebrates, and fruits. Neocortex was greatly expanded, and included an array of cortical areas that characterize neocortex of all living primates. Specializations of the visual system included new visual areas that contributed to a dorsal stream of visuomotor processing in a greatly enlarged region of posterior parietal cortex and an expanded motor system and the addition of a ventral premotor area. Higher visual areas in a large temporal lobe facilitated object recognition, and frontal cortex, included granular prefrontal cortex. Auditory cortex included the primary and secondary auditory areas that characterize prosimian and anthropoid primates today. As anthropoids emerged as diurnal primates, the visual system specialized for detailed foveal vision. Other adaptations included an expansion of prefrontal cortex and insular cortex. The human and chimpanzee-bonobo lineages diverged some 6–8 million years ago with brains that were about one-third the size of modern humans. Over the last two million years, the brains of our more recent ancestors increased greatly in size, especially in the prefrontal, posterior parietal, lateral temporal, and insular regions. Specialization of the two cerebral hemispheres for related, but different functions became pronounced, and language and other impressive cognitive abilities emerged.
doi:10.1002/wcs.1206
PMCID: PMC3606080  PMID: 23529256
9.  Temporal Reliability and Lateralization of the Resting-State Language Network 
PLoS ONE  2014;9(1):e85880.
The neural processing loop of language is complex but highly associated with Broca's and Wernicke's areas. The left dominance of these two areas was the earliest observation of brain asymmetry. It was demonstrated that the language network and its functional asymmetry during resting state were reproducible across institutions. However, the temporal reliability of resting-state language network and its functional asymmetry are still short of knowledge. In this study, we established a seed-based resting-state functional connectivity analysis of language network with seed regions located at Broca's and Wernicke's areas, and investigated temporal reliability of language network and its functional asymmetry. The language network was found to be temporally reliable in both short- and long-term. In the aspect of functional asymmetry, the Broca's area was found to be left lateralized, while the Wernicke's area is mainly right lateralized. Functional asymmetry of these two areas revealed high short- and long-term reliability as well. In addition, the impact of global signal regression (GSR) on reliability of the resting-state language network was investigated, and our results demonstrated that GSR had negligible effect on the temporal reliability of the resting-state language network. Our study provided methodology basis for future cross-culture and clinical researches of resting-state language network and suggested priority of adopting seed-based functional connectivity for its high reliability.
doi:10.1371/journal.pone.0085880
PMCID: PMC3901661  PMID: 24475058
10.  Broca's Region: Novel Organizational Principles and Multiple Receptor Mapping 
PLoS Biology  2010;8(9):e1000489.
A novel map of Broca's language region is proposed based on transmitter receptor distributions as functionally relevant molecular markers. It sheds new light on the relation between anatomy and functional segregation.
There is a considerable contrast between the various functions assigned to Broca's region and its relatively simple subdivision into two cytoarchitectonic areas (44 and 45). Since the regional distribution of transmitter receptors in the cerebral cortex has been proven a powerful indicator of functional diversity, the subdivision of Broca's region was analyzed here using a multireceptor approach. The distribution patterns of six receptor types using in vitro receptor autoradiography revealed previously unknown areas: a ventral precentral transitional cortex 6r1, dorsal and ventral areas 44d and 44v, anterior and posterior areas 45a and 45p, and areas op8 and op9 in the frontal operculum. A significant lateralization of receptors was demonstrated with respect to the cholinergic M2 receptor, particularly in area 44v+d. We propose a new concept of the anterior language region, which elucidates the relation between premotor cortex, prefrontal cortex, and Broca's region. It offers human brain homologues to the recently described subdivision of area 45, and the segregation of the ventral premotor cortex in macaque brains. The results provide a novel structural basis of the organization of language regions in the brain.
Author Summary
Broca's region is involved in many aspects of language processing in the brain. Such detailed functional diversity, however, is in contrast to its classical anatomical subdivision into only two cortical areas. Since the regional distribution of neurotransmitter receptors has been proven to be a powerful indicator of functional segregation, we revised the subdivision of Broca's region by analyzing the distribution of six different receptor types in the human brain. On the basis of these results, we propose a novel map of Broca's and neighboring regions with several, previously unknown areas. Moreover, a significant left-sided interhemispheric asymmetry of receptors was found, mainly for the cholinergic muscarinic M2 type. This asymmetry correlates with the well-known left-sided dominance for language. Finally, we present a model of the molecular organization of the anterior human language region and neighboring prefrontal and motor areas on the basis of similarities in their receptor patterns. This model contributes to our understanding of the relation between motor areas and classical Broca region. Our results are important for future studies of the functional segregation and the role of mirror neurons in the human brain, and are relevant for revealing homologies between human and macaque brains.
doi:10.1371/journal.pbio.1000489
PMCID: PMC2943440  PMID: 20877713
11.  The neural and cognitive correlates of aimed throwing in chimpanzees: a magnetic resonance image and behavioural study on a unique form of social tool use 
It has been hypothesized that neurological adaptations associated with evolutionary selection for throwing may have served as a precursor for the emergence of language and speech in early hominins. Although there are reports of individual differences in aimed throwing in wild and captive apes, to date there has not been a single study that has examined the potential neuroanatomical correlates of this very unique tool-use behaviour in non-human primates. In this study, we examined whether differences in the ratio of white (WM) to grey matter (GM) were evident in the homologue to Broca's area as well as the motor-hand area of the precentral gyrus (termed the KNOB) in chimpanzees that reliably throw compared with those that do not. We found that the proportion of WM in Broca's homologue and the KNOB was significantly higher in subjects that reliably throw compared with those that do not. We further found that asymmetries in WM within both brain regions were larger in the hemisphere contralateral to the chimpanzee's preferred throwing hand. We also found that chimpanzees that reliably throw show significantly better communication abilities than chimpanzees that do not. These results suggest that chimpanzees that have learned to throw have developed greater cortical connectivity between primary motor cortex and the Broca's area homologue. It is suggested that during hominin evolution, after the split between the lines leading to chimpanzees and humans, there was intense selection on increased motor skills associated with throwing and that this potentially formed the foundation for left hemisphere specialization associated with language and speech found in modern humans.
doi:10.1098/rstb.2011.0195
PMCID: PMC3223792  PMID: 22106425
throwing; Broca's area; chimpanzees
12.  Genes Expressed in Specific Areas of the Human Fetal Cerebral Cortex Display Distinct Patterns of Evolution 
PLoS ONE  2011;6(3):e17753.
The developmental mechanisms through which the cerebral cortex increased in size and complexity during primate evolution are essentially unknown. To uncover genetic networks active in the developing cerebral cortex, we combined three-dimensional reconstruction of human fetal brains at midgestation and whole genome expression profiling. This novel approach enabled transcriptional characterization of neurons from accurately defined cortical regions containing presumptive Broca and Wernicke language areas, as well as surrounding associative areas. We identified hundreds of genes displaying differential expression between the two regions, but no significant difference in gene expression between left and right hemispheres. Validation by qRTPCR and in situ hybridization confirmed the robustness of our approach and revealed novel patterns of area- and layer-specific expression throughout the developing cortex. Genes differentially expressed between cortical areas were significantly associated with fast-evolving non-coding sequences harboring human-specific substitutions that could lead to divergence in their repertoires of transcription factor binding sites. Strikingly, while some of these sequences were accelerated in the human lineage only, many others were accelerated in chimpanzee and/or mouse lineages, indicating that genes important for cortical development may be particularly prone to changes in transcriptional regulation across mammals. Genes differentially expressed between cortical regions were also enriched for transcriptional targets of FoxP2, a key gene for the acquisition of language abilities in humans. Our findings point to a subset of genes with a unique combination of cortical areal expression and evolutionary patterns, suggesting that they play important roles in the transcriptional network underlying human-specific neural traits.
doi:10.1371/journal.pone.0017753
PMCID: PMC3060818  PMID: 21445258
13.  Analysis of Chimpanzee History Based on Genome Sequence Alignments 
PLoS Genetics  2008;4(4):e1000057.
Population geneticists often study small numbers of carefully chosen loci, but it has become possible to obtain orders of magnitude for more data from overlaps of genome sequences. Here, we generate tens of millions of base pairs of multiple sequence alignments from combinations of three western chimpanzees, three central chimpanzees, an eastern chimpanzee, a bonobo, a human, an orangutan, and a macaque. Analysis provides a more precise understanding of demographic history than was previously available. We show that bonobos and common chimpanzees were separated ∼1,290,000 years ago, western and other common chimpanzees ∼510,000 years ago, and eastern and central chimpanzees at least 50,000 years ago. We infer that the central chimpanzee population size increased by at least a factor of 4 since its separation from western chimpanzees, while the western chimpanzee effective population size decreased. Surprisingly, in about one percent of the genome, the genetic relationships between humans, chimpanzees, and bonobos appear to be different from the species relationships. We used PCR-based resequencing to confirm 11 regions where chimpanzees and bonobos are not most closely related. Study of such loci should provide information about the period of time 5–7 million years ago when the ancestors of humans separated from those of the chimpanzees.
Author Summary
Studies of population history traditionally examine a small number of genetic regions in many individuals; however, with genome sequencing technologies it is possible to assemble data sets with thousands more aligned sequences albeit in fewer individuals. To explore whether such data can provide useful insights about population history, we assembled large-scale data sets consisting of overlaps of random genome sequencing reads from chimpanzees and bonobos. Analysis of these data finds that bonobos and chimpanzees split from each other about 1.29 million years ago, western and central chimpanzees about 0.51 million years ago, and eastern and central chimpanzees at least 50,000 years ago. We find that the chimpanzee population has fluctuated significantly in size over the past half million years, with the central chimpanzee population size expanding dramatically, and the western chimpanzee population size contracting. Surprisingly, we also find that there are widespread regions of the genome where chimpanzees and bonobos are less closely related to each other than any of them are to humans. In these regions, chimpanzees and bonobos share a common genetic ancestor dating back to speciation from humans, providing a new source of information about that evolutionary event.
doi:10.1371/journal.pgen.1000057
PMCID: PMC2278377  PMID: 18421364
14.  A Large-Scale Investigation of Lateralization in Cortical Anatomy and Word Reading: Are There Sex Differences? 
Neuropsychology  2009;23(2):210-222.
Although left hemisphere language specialization is one of the most widely reported findings in human neuropsychology, some studies have found evidence for more bilateral language organization in women. We report findings of a large scale, multi-task investigation of sex differences in both structural asymmetries and lateralization of word reading. Two hundred participants were tested in eight divided visual field lexical tasks, and each received a structural MRI scan. We examined whether there was evidence for sex differences in overall measures of neuroanatomical and behavioral lateralization, in specific language tasks and brain regions, and in variation in asymmetry within and across tasks and brain regions. There was very little evidence for sex differences on any behavioral measure. The few indications of sex differences in the current report accounted for 2% or less of the individual variation in asymmetry and could not be replicated in independent subsamples. No sex differences were observed in the asymmetry of structures in Broca’s and Wernicke’s area such as pars triangularis, pars opercularis, the planum temporale, planum parietale, or Heschl’s gyrus. There were also no sex differences in the variability of neuroanatomical asymmetries within or between brain regions. However, a significant relationship between planum temporale and behavioral asymmetry was restricted to men.
doi:10.1037/a0014265
PMCID: PMC3086359  PMID: 19254094
sex differences; cerebral asymmetry; word reading; planum temporale; neuroanatomical asymmetry
15.  Neuroanatomical Correlates of Handedness for Tool Use in Chimpanzees (Pan troglodytes) 
Psychological science  2007;18(11):971-977.
It has been hypothesized that cognitive mechanisms underlying lateralized complex motor actions associated with tool use in chimpanzees may have set the stage for the evolution of left-hemisphere specialization for language and speech in humans. Here we report evidence that asymmetries in the homologues to Broca’s and Wernicke’s areas are associated with handedness for tool use in chimpanzees. These results suggest that the neural substrates of tool use may have served as a preadaptation for the evolution of language and speech in modern humans.
doi:10.1111/j.1467-9280.2007.02011.x
PMCID: PMC2662703  PMID: 17958711
16.  The Chimpanzee Brain Shows Human-Like Perisylvian Asymmetries in White Matter 
Modern neuroimaging technologies allow scientists to uncover inter-species differences and similarities in hemispheric asymmetries that may shed light onto the origin of brain asymmetry and its functional correlates. We analyzed asymmetries in white to grey matter ratios of the lateral aspect of the lobes of the brains of chimpanzees. We found marked leftward asymmetries for all lobar regions. This asymmetry was particularly pronounced in the frontal region and was found to be related to handedness for communicative manual gestures as well as for tool use. These results point to a continuity in asymmetry patterns between the human and chimpanzee brain, and support the notion that the anatomical substrates for lateralization of communicative functions and complex manipulative activities may have been present in the common hominid ancestor.
doi:10.1111/j.1460-9568.2009.06830.x
PMCID: PMC4195238  PMID: 19614754
hemispheric asymmetry; white matter; gray matter; tool use; handedness; chimpanzee
17.  Communicative Signaling Activates ‘Broca’s’ Homolog in Chimpanzees 
Current biology : CB  2008;18(5):343-348.
Summary
Broca’s area, a cerebral cortical area located in the inferior frontal gyrus (IFG) of the human brain, has been identified as one of several critical regions associated with the motor planning and execution of language. Anatomically, Broca’s area is most often larger in the left hemisphere, and functional imaging studies in humans indicate significant left-lateralized patterns of activation during language-related tasks [1–3]. If, and to what extent, nonhuman primates, particularly chimpanzees, possess a homologous region that is involved in the production of their own communicative signals remains unknown. Here, we show that portions of the IFG as well as other cortical and subcortical regions in chimpanzees are active during the production of communicative signals. These findings are the first to provide direct evidence of the neuroanatomical structures associated with the production of communicative behaviors in chimpanzees. Significant activation in the left IFG in conjunction with other cortical and subcortical brain areas during the production of communicative signals in chimpanzees suggests that the neurological substrates underlying language production in the human brain may have been present in the common ancestor of humans and chimpanzees.
doi:10.1016/j.cub.2008.01.049
PMCID: PMC2665181  PMID: 18308569
18.  Neuroanatomical Localization of the Motor Hand Area With Magnetic Resonance Imaging: The Left Hemisphere Is Larger in Great Apes 
Behavioral neuroscience  2001;115(5):1159-1164.
Magnetic resonance images of the brain were obtained from 2 gorillas (Gorilla gorilla gorilla), 4 orangutans (Pongo pygmaeus), 14 chimpanzees (Pan troglodytes), and 4 bonobos (Pan paniscus). The region on the motor cortex of humans identified as responsible for motor skill of the hand (the “knob”) was identified in this sample on consecutive 1-mm axial scans. The shape of the knob area was traced on each scan from both hemispheres, and the area from all scans was summed to calculate the knob volume. The width of the knob was also measured and correlated highly with knob volume. A significant population-level leftward asymmetry in the volume and width of the knob was revealed (p < .05). Species differences in knob asymmetry and overall volume were not significant, but the variability in overall volume between species was substantial. Selection for the evolution of a neuroanatomical representation of the hand in primates and an evolutionary trend toward population-level right handedness are discussed.
PMCID: PMC2001157  PMID: 11584929
19.  Left Hemisphere Specialization for Oro-Facial Movements of Learned Vocal Signals by Captive Chimpanzees 
PLoS ONE  2008;3(6):e2529.
Background
The left hemisphere of the human brain is dominant in the production of speech and signed language. Whether similar lateralization of function for communicative signal production is present in other primates remains a topic of considerable debate. In the current study, we examined whether oro-facial movements associated with the production of learned attention-getting sounds are differentially lateralized compared to facial expressions associated with the production of species-typical emotional vocalizations in chimpanzees.
Methodology/ Principal Findings
Still images captured from digital video were used to quantify oro-facial asymmetries in the production of two attention-getting sounds and two species-typical vocalizations in a sample of captive chimpanzees. Comparisons of mouth asymmetries during production of these sounds revealed significant rightward biased asymmetries for the attention-getting sounds and significant leftward biased asymmetries for the species-typical sounds.
Conclusions/Significance
These results suggest that the motor control of oro-facial movements associated with the production of learned sounds is lateralized to the left hemisphere in chimpanzees. Furthermore, the findings suggest that the antecedents for lateralization of human speech may have been present in the common ancestor of chimpanzees and humans ∼5 mya and are not unique to the human lineage.
doi:10.1371/journal.pone.0002529
PMCID: PMC2429967  PMID: 18575610
20.  Neuropeptide Y-immunoreactive neurons in the cerebral cortex of humans and other haplorrhine primates 
American journal of primatology  2012;75(5):415-424.
We examined the distribution of neurons immunoreactive for neuropeptide Y (NPY) in the posterior part of the superior temporal cortex (Brodmann's area 22 or area Tpt) of humans and nonhuman haplorrhine primates. NPY has been implicated in learning and memory and the density of NPY-expressing cortical neurons and axons is reduced in depression, bipolar disorder, schizophrenia, and Alzheimer's disease. Due to the role that NPY plays in both cognition and neurodegenerative diseases, we tested the hypothesis that the density of cortical and interstitial neurons expressing NPY was increased in humans relative to other primate species. The study sample included great apes (chimpanzee and gorilla), Old World monkeys (pigtailed macaque, moor macaque, and baboon) and New World monkeys (squirrel monkey and capuchin). Stereologic methods were used to estimate the density of NPY-immunoreactive (-ir) neurons in layers I-VI of area Tpt and the subjacent white matter. Adjacent Nissl-stained sections were used to calculate local densities of all neurons. The ratio of NPY-ir neurons to total neurons within area Tpt and the total density of NPY-ir neurons within the white matter were compared among species. Overall, NPY-ir neurons represented only an average of 0.006% of the total neuron population. While there were significant differences among species, phylogenetic trends in NPY-ir neuron distributions were not observed and humans did not differ from other primates. However, variation among species warrants further investigation into the distribution of this neuromodulator system.
doi:10.1002/ajp.22082
PMCID: PMC3560302  PMID: 23042407
Wernicke's area; area Tpt; area 22; evolution; NPY
21.  Functional rearrangement of language areas in patients with tumors of the central nervous system using functional magnetic resonance imaging 
Polish Journal of Radiology  2012;77(3):39-45.
Summary
Background:
The aim of this study was to determine the reorganization of the language areas in patients with tumors located near speech centers using functional magnetic resonance imaging (fMRI).
Material/Methods:
fMRI was performed prior to the surgical treatment of 11 right-handed patients with tumors located close to the Broca’s or Wernicke’s areas of the left hemisphere. The analysis included a record of the activity in four regions of interest (ROIs): Broca’s and Wernicke’s areas, and their anatomic homologues in the right hemisphere. For each patient a regional lateralization index was calculated separately for Broca’s area versus its right-hemisphere homolog and Wernicke’s area versus its right-hemisphere homolog. The results were correlated with the histopathological type of the tumor and its size.
Results:
Our fMRI examinations showed activation of the Broca’s area in the right hemisphere in 3/4 cases of low grade gliomas (LGG) localized in the left frontal lobe. In one case of the high grade glioma (HGG) only the left hemisphere Broca’s area was activated (LI=1). Activation in Wernicke’s area in both hemispheres was obtained irrespective of the size and histological type of the tumor.
All tumors localized in the left temporal lobe were HGG. We obtained activation only in the right hemisphere Wernicke’s area in 4/5 of the cases. In 4/5 of the cases activation in Broca’s area was present- in 2 cases in the left hemisphere, in 1 case in the right hemisphere and in 1 case bilateral.
Conclusions:
The presence of a neoplastic lesion in close topographic relationship to language areas induces their functional reorganization.
fMRI is an useful method for determination of language areas localization in pre-operative planning. HGG tumors localized near Wernicke’s area lead to transfer its function to the healthy hemisphere and/or to decreased activity in the affected hemisphere.
PMCID: PMC3447432  PMID: 23049580
neuroplasticity; language lateralization; functional magnetic resonance imaging; Broca; Wernicke
22.  The sound of one-hand clapping: handedness and perisylvian neural correlates of a communicative gesture in chimpanzees 
Whether lateralization of communicative signalling in non-human primates might constitute prerequisites of hemispheric specialization for language is unclear. In the present study, we examined (i) hand preference for a communicative gesture (clapping in 94 captive chimpanzees from two research facilities) and (ii) the in vivo magnetic resonance imaging brain scans of 40 of these individuals. The preferred hand for clapping was defined as the one in the upper position when the two hands came together. Using computer manual tracing of regions of interest, we measured the neuroanatomical asymmetries for the homologues of key language areas, including the inferior frontal gyrus (IFG) and planum temporale (PT). When considering the entire sample, there was a predominance of right-handedness for clapping and the distribution of right- and left-handed individuals did not differ between the two facilities. The direction of hand preference (right- versus left-handed subjects) for clapping explained a significant portion of variability in asymmetries of the PT and IFG. The results are consistent with the view that gestural communication in the common ancestor may have been a precursor of language and its cerebral substrates in modern humans.
doi:10.1098/rspb.2011.2485
PMCID: PMC3311905  PMID: 22217719
handedness; gestural communication; hemispheric specialization; origins of language; primates
23.  Interhemispheric and intrahemispheric language reorganization in complex partial epilepsy 
Neurology  2009;72(21):1830-1836.
Objective:
To investigate interhemispheric and intrahemispheric reorganization in patients with localization-related epilepsy.
Method:
We studied 50 patients with a left hemispheric focus and 20 normal right-handed controls with a 3T echoplanar imaging blood oxygen level dependent functional MRI auditory-based word definition decision task. Data were analyzed using SPM 2. Using region of interest for Broca and Wernicke areas and an asymmetry index (AI), patients were categorized as left language (LL; AI ≥0.20) or atypical language (AL; AI <0.20) for region. The point maxima activation for normal controls (p <0.05 corrected FDR) was identified in Broca and midtemporal regions and then used as a point of reference for individual point maxima identified at p < 0.001, uncorrected.
Results:
Patient groups showed increased frequency of having activation in right homologues. Activation in AL groups occurred in homologous right regions; distances for point maxima activation in homologous regions were the same as point maxima distances in normal control activation in left regions. Distances for LL patient in left regions showed a trend for differences for midtemporal gyrus (6 mm posterior, 3 mm superior) but variability around mean difference distance was significant. There was no effect of age at epilepsy onset, duration, or pathology on activation maxima.
Conclusions:
Right hemisphere language regions in patients with left hemispheric focus are homologues of left hemisphere Broca and broadly defined Wernicke areas. We found little evidence for intrahemispheric reorganization in patients with left hemisphere epilepsy who remain left language dominant by these methods.
GLOSSARY
= asymmetry index;
= atypical language;
= Brodmann area;
= electrocortical stimulation;
= functional MRI;
= inferior frontal gyrus;
= left hemispheric focus;
= left language;
= multivariate analysis of variance;
= midtemporal gyrus;
= superior temporal gyrus;
= superior temporal sulcus.
doi:10.1212/WNL.0b013e3181a7114b
PMCID: PMC2690987  PMID: 19470965
24.  Sex differences in asymmetry of the planum parietale in chimpanzees (Pan troglodytes) 
Behavioural brain research  2007;184(2):185-191.
Magnetic resonance images were collected in 76 chimpanzees and the sylvian fissure was examined for the presence of a posterior bifurcation. A bilateral bifurcation of the sylvian fissure into an ascending and descending ramus was identified in 58 of the subjects. The posterior ascending ramus was measured in both hemispheres in order to evaluate the presence, magnitude, and direction of a planum parietale asymmetry. Statistical analysis revealed a main effect for sex. Specifically, females showed a significant rightward bias, whereas males did not. Moreover, an examination of posterior bifurcation patterns of the sylvian fissure revealed differences between the left and right hemispheres. In humans, subject handedness and sex have been found to have an effect on planum parietale asymmetry. To determine if this was also the case in our chimpanzee subjects, we evaluated whether or not planum parietale asymmetry was related to subject handedness. Although subject handedness was not directly related to planum parietale asymmetry quotients, significant differences in the pattern of posterior bifurcation of the sylvian fissure were found between males and females. These results support the view that asymmetries in the peri-sylvian language areas were present in the common ancestor of humans and chimpanzees.
doi:10.1016/j.bbr.2007.07.025
PMCID: PMC2141691  PMID: 17765336
planum parietale; chimpanzee; brain asymmetry; lateralization; handedness; language
25.  Diffuse Cerebral Language Representation in Tuberous Sclerosis Complex 
Epilepsy research  2012;104(1-2):125-133.
Introduction
Tuberous sclerosis complex (TSC) is a multisystem genetic disorder affecting multiple organs, including the brain, and very often associated with epileptic activity. Language acquisition and development seems to be altered in a significant proportion of patients with TSC. In the present study, we used magnetoencephalography (MEG) to investigate spatiotemporal cerebral language processing in subjects with TSC and epilepsy during a reading semantic decision task, compared to healthy control participants.
Methods
Fifteen patients with TSC and 31 healthy subjects performed a lexico-semantic decision task during MEG recording. Minimum-norm estimates (MNE) were computed allowing identification of cerebral generators of language evoked fields (EF) in each subject.
Results
Source analysis of the language EF demonstrated early bilateral medial occipital activation (125ms) followed by a fusiform gyrus activation around 135ms. At 270ms post stimuli presentation, a strong cerebral activation was recorded in the left basal temporal language area. Finally, cerebral activations were measured in Wernicke’s area followed by Broca’s area. The healthy control group showed larger and earlier language activations in Broca and Wernicke’s areas compared to TSC patients. Moreover, cerebral activation from Broca’s area was greater than activation from Wernicke’s area in both groups, but this difference between anterior and posterior regions was smaller in the TSC group. Finally, the activation latency difference between Broca and Wernicke’s areas was greater in healthy controls than in TSC patients, which shows that activations in these areas are more serial in control subjects compared to TSC patients in whom activations occur more simultaneously.
Conclusions
This is the first study to investigate cerebral language pattern in patients with TSC. Compared to healthy controls, atypical neuromagnetic language responses may reflect cerebral reorganization in these patients in response to early epileptogenic activity or presence at birth of multiple brain lesions.
doi:10.1016/j.eplepsyres.2012.09.011
PMCID: PMC3574215  PMID: 23092910
magnetoencephalography (MEG); source localization; distributed source model; tuberous sclerosis complex (TSC); epilepsy; language

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