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1.  Cognitive control and its impact on recovery from aphasic stroke 
Brain  2013;137(1):242-254.
Aphasic deficits are usually only interpreted in terms of domain-specific language processes. However, effective human communication and tests that probe this complex cognitive skill are also dependent on domain-general processes. In the clinical context, it is a pragmatic observation that impaired attention and executive functions interfere with the rehabilitation of aphasia. One system that is important in cognitive control is the salience network, which includes dorsal anterior cingulate cortex and adjacent cortex in the superior frontal gyrus (midline frontal cortex). This functional imaging study assessed domain-general activity in the midline frontal cortex, which was remote from the infarct, in relation to performance on a standard test of spoken language in 16 chronic aphasic patients both before and after a rehabilitation programme. During scanning, participants heard simple sentences, with each listening trial followed immediately by a trial in which they repeated back the previous sentence. Listening to sentences in the context of a listen–repeat task was expected to activate regions involved in both language-specific processes (speech perception and comprehension, verbal working memory and pre-articulatory rehearsal) and a number of task-specific processes (including attention to utterances and attempts to overcome pre-response conflict and decision uncertainty during impaired speech perception). To visualize the same system in healthy participants, sentences were presented to them as three-channel noise-vocoded speech, thereby impairing speech perception and assessing whether this evokes domain general cognitive systems. As expected, contrasting the more difficult task of perceiving and preparing to repeat noise-vocoded speech with the same task on clear speech demonstrated increased activity in the midline frontal cortex in the healthy participants. The same region was activated in the aphasic patients as they listened to standard (undistorted) sentences. Using a region of interest defined from the data on the healthy participants, data from the midline frontal cortex was obtained from the patients. Across the group and across different scanning sessions, activity correlated significantly with the patients’ communicative abilities. This correlation was not influenced by the sizes of the lesion or the patients’ chronological ages. This is the first study that has directly correlated activity in a domain general system, specifically the salience network, with residual language performance in post-stroke aphasia. It provides direct evidence in support of the clinical intuition that domain-general cognitive control is an essential factor contributing to the potential for recovery from aphasic stroke.
PMCID: PMC3891442  PMID: 24163248
aphasia; salience; cingulate; executive; functional MRI
2.  The cognitive organization of music knowledge: a clinical analysis 
Brain  2010;133(4):1200-1213.
Despite much recent interest in the clinical neuroscience of music processing, the cognitive organization of music as a domain of non-verbal knowledge has been little studied. Here we addressed this issue systematically in two expert musicians with clinical diagnoses of semantic dementia and Alzheimer’s disease, in comparison with a control group of healthy expert musicians. In a series of neuropsychological experiments, we investigated associative knowledge of musical compositions (musical objects), musical emotions, musical instruments (musical sources) and music notation (musical symbols). These aspects of music knowledge were assessed in relation to musical perceptual abilities and extra-musical neuropsychological functions. The patient with semantic dementia showed relatively preserved recognition of musical compositions and musical symbols despite severely impaired recognition of musical emotions and musical instruments from sound. In contrast, the patient with Alzheimer’s disease showed impaired recognition of compositions, with somewhat better recognition of composer and musical era, and impaired comprehension of musical symbols, but normal recognition of musical emotions and musical instruments from sound. The findings suggest that music knowledge is fractionated, and superordinate musical knowledge is relatively more robust than knowledge of particular music. We propose that music constitutes a distinct domain of non-verbal knowledge but shares certain cognitive organizational features with other brain knowledge systems. Within the domain of music knowledge, dissociable cognitive mechanisms process knowledge derived from physical sources and the knowledge of abstract musical entities.
PMCID: PMC2850578  PMID: 20142334
music; semantic memory; dementia; semantic dementia; Alzheimer’s disease
3.  Anterior temporal lobe connectivity correlates with functional outcome after aphasic stroke 
Brain  2009;132(12):3428-3442.
Focal brain lesions are assumed to produce language deficits by two basic mechanisms: local cortical dysfunction at the lesion site, and remote cortical dysfunction due to disruption of the transfer and integration of information between connected brain regions. However, functional imaging studies investigating language outcome after aphasic stroke have tended to focus only on the role of local cortical function. In this positron emission tomography functional imaging study, we explored relationships between language comprehension performance after aphasic stroke and the functional connectivity of a key speech-processing region in left anterolateral superior temporal cortex. We compared the organization of left anterolateral superior temporal cortex functional connections during narrative speech comprehension in normal subjects with left anterolateral superior temporal cortex connectivity in a group of chronic aphasic stroke patients. We then evaluated the language deficits associated with altered left anterolateral superior temporal cortex connectivity in aphasic stroke. During normal narrative speech comprehension, left anterolateral superior temporal cortex displayed positive functional connections with left anterior basal temporal cortex, left inferior frontal gyrus and homotopic cortex in right anterolateral superior temporal cortex. As a group, aphasic patients demonstrated a selective disruption of the normal functional connection between left and right anterolateral superior temporal cortices. We observed that deficits in auditory single word and sentence comprehension correlated both with the degree of disruption of left-right anterolateral superior temporal cortical connectivity and with local activation in the anterolateral superior temporal cortex. Subgroup analysis revealed that aphasic patients with preserved positive intertemporal connectivity displayed better receptive language function; these patients also showed greater than normal left inferior frontal gyrus activity, suggesting a possible ‘top-down’ compensatory mechanism. These results demonstrate that functional connectivity between anterolateral superior temporal cortex and right anterior superior temporal cortex is a marker of receptive language outcome after aphasic stroke, and illustrate that language system organization after focal brain lesions may be marked by complex signatures of altered local and pathway-level function.
PMCID: PMC2792371  PMID: 19903736
aphasia; post-stroke recovery; functional neuroimaging; neural networks; anterior temporal lobe
4.  Word-finding difficulty: a clinical analysis of the progressive aphasias 
Brain : a journal of neurology  2007;131(Pt 1):8-38.
The patient with word-finding difficulty presents a common and challenging clinical problem. The complaint of ‘word-finding difficulty’ covers a wide range of clinical phenomena and may signify any of a number of distinct pathophysiological processes. Although it occurs in a variety of clinical contexts, word-finding difficulty generally presents a diagnostic conundrum when it occurs as a leading or apparently isolated symptom, most often as the harbinger of degenerative disease: the progressive aphasias. Recent advances in the neurobiology of the focal, language-based dementias have transformed our understanding of these processes and the ways in which they breakdown in different diseases, but translation of this knowledge to the bedside is far from straightforward. Speech and language disturbances in the dementias present unique diagnostic and conceptual problems that are not fully captured by classical models derived from the study of vascular and other acute focal brain lesions. This has led to a reformulation of our understanding of how language is organized in the brain. In this review we seek to provide the clinical neurologist with a practical and theoretical bridge between the patient presenting with word-finding difficulty in the clinic and the evidence of the brain sciences. We delineate key illustrative speech and language syndromes in the degenerative dementias, compare these syndromes with the syndromes of acute brain damage, and indicate how the clinical syndromes relate to emerging neurolinguistic, neuroanatomical and neurobiological insights. We propose a conceptual framework for the analysis of word-finding difficulty, in order both better to define the patient's complaint and its differential diagnosis for the clinician and to identify unresolved issues as a stimulus to future work.
PMCID: PMC2373641  PMID: 17947337
aphasia; progressive aphasia; anomia; dementia; speech and language

Results 1-4 (4)