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1.  Disentangling spatial perception and spatial memory in the hippocampus: a univariate and multivariate pattern analysis fMRI study 
Journal of cognitive neuroscience  2012;25(4):10.1162/jocn_a_00301.
Although the role of the hippocampus in spatial cognition is well accepted, it is unclear whether its involvement is restricted to the mnemonic domain or also extends to perception. We used functional magnetic resonance imaging (fMRI) to scan neurologically healthy participants during a scene oddity judgment task that placed no explicit demand on long-term memory. Crucially, a surprise recognition test was administered after scanning so that each trial could be categorized not only according to oddity accuracy but also subsequent memory. Univariate analyses showed significant hippocampal activity in association with correct oddity judgment, whereas greater parahippocampal place area (PPA) activity was observed during incorrect oddity trials, both irrespective of subsequent recognition performance. Consistent with this, multivariate pattern analyses revealed that a linear support vector machine was able to distinguish correct from incorrect oddity trials on the basis of activity in voxels within the hippocampus or PPA. Although no significant regions of activity were identified by univariate analyses in association with memory performance, a classifier was able to predict subsequent memory using voxels in either the hippocampus or PPA. Our findings are consistent with the idea that the hippocampus is important for processes beyond long-term declarative memory and that this structure may also play a role in complex spatial perception.
PMCID: PMC3807938  PMID: 23016766
2.  A Potential Spatial Working Memory Training Task to Improve Both Episodic Memory and Fluid Intelligence 
PLoS ONE  2012;7(11):e50431.
One current challenge in cognitive training is to create a training regime that benefits multiple cognitive domains, including episodic memory, without relying on a large battery of tasks, which can be time-consuming and difficult to learn. By giving careful consideration to the neural correlates underlying episodic and working memory, we devised a computerized working memory training task in which neurologically healthy participants were required to monitor and detect repetitions in two streams of spatial information (spatial location and scene identity) presented simultaneously (i.e. a dual n-back paradigm). Participants’ episodic memory abilities were assessed before and after training using two object and scene recognition memory tasks incorporating memory confidence judgments. Furthermore, to determine the generalizability of the effects of training, we also assessed fluid intelligence using a matrix reasoning task. By examining the difference between pre- and post-training performance (i.e. gain scores), we found that the trainers, compared to non-trainers, exhibited a significant improvement in fluid intelligence after 20 days. Interestingly, pre-training fluid intelligence performance, but not training task improvement, was a significant predictor of post-training fluid intelligence improvement, with lower pre-training fluid intelligence associated with greater post-training gain. Crucially, trainers who improved the most on the training task also showed an improvement in recognition memory as captured by d-prime scores and estimates of recollection and familiarity memory. Training task improvement was a significant predictor of gains in recognition and familiarity memory performance, with greater training improvement leading to more marked gains. In contrast, lower pre-training recollection memory scores, and not training task improvement, led to greater recollection memory performance after training. Our findings demonstrate that practice on a single working memory task can potentially improve aspects of both episodic memory and fluid intelligence, and that an extensive training regime with multiple tasks may not be necessary.
PMCID: PMC3508978  PMID: 23209740
3.  Human medial temporal lobe damage can disrupt the perception of single objects 
The idea that the medial temporal lobe (MTL), traditionally viewed as an exclusive memory system, may also subserve higher-order perception has been debated fiercely. To support this suggestion, monkey and human lesion studies have demonstrated that perirhinal cortex damage impairs complex object discrimination. The interpretation of these findings has, however, been disputed since these impairments may reflect a primary deficit in MTL-mediated working memory processes or, in the case of human patients, undetected damage to visual processing regions beyond the MTL. To address these issues, this study investigated object perception in two human amnesic patients who were chosen on the basis of their lesion locations and suitability for detailed neuroimaging investigation. A neuropsychological task with minimal working memory demands was administered in which participants assessed the structural coherency of single novel objects. Critically, only the patient with perirhinal atrophy was impaired. Moreover, volumetric and functional neuroimaging data demonstrated that this deficit cannot be attributed to the dysfunction of visual cortical areas. Additional analyses of eye-movement patterns during the perceptual task revealed an inability of this patient to detect structural incoherency consistently. This study uses a combination of techniques to provide strong evidence that the perirhinal cortex subserves perception and suggests that the MTL perceptual-mnemonic debate cannot be dismissed on the basis of anatomy or a working memory impairment.
PMCID: PMC3079896  PMID: 20463221
Memory; Amnesia; Hippocampus; Parahippocampal; Imaging; Eye movement
4.  Investigating the Interaction between Spatial Perception and Working Memory in the Human Medial Temporal Lobe 
Journal of cognitive neuroscience  2010;22(12):2823-2835.
There has been considerable debate surrounding the functions of the medial temporal lobe (MTL). Although this region has been traditionally thought to subserve long-term declarative memory only, recent evidence suggests a role in short-term working memory and even higher-order perception. To investigate this issue, functional neuroimaging was used to investigate the involvement of the MTL in spatial scene perception and working memory. Healthy participants were scanned during a working memory task incorporating two factors of working memory (high vs. low demand) and spatial processing (complex vs. simple). It was found that an increase in spatial processing demand produced significantly greater activity in the posterior hippocampus and parahippocampal cortex irrespective of whether working memory demand was high or low. In contrast, there was no region within the MTL that increased significantly in activity during both the complex and simple spatial processing conditions when working memory demand was increased. There was, however, a significant interaction effect between spatial processing and working memory in the right posterior hippocampus and parahippocampal cortex bilaterally: an increase in working memory demand produced a significant increase in activity in these areas during the complex, but not simple, spatial processing conditions. These findings suggest while there may be a role for the MTL in both stimulus processing and working memory, increasing the latter does not necessarily increase posterior MTL involvement. We suggest that these structures may play a critical role in processing complex spatial representations, which, in turn, may form the basis of short- and long-term mnemonic processes.
PMCID: PMC2929461  PMID: 19925184
5.  Fornix microstructure correlates with recollection but not familiarity memory 
The fornix is the main tract between the medial temporal lobe (MTL) and medial diencephalon, both of which are critical for episodic memory. The precise involvement of the fornix in memory, however, has been difficult to ascertain since damage to this tract in human amnesics is invariably accompanied by atrophy to surrounding structures. We used diffusion-weighted imaging to investigate whether individual differences in fornix white matter microstructure in neurologically healthy participants were related to differences in memory as assessed by two recognition tasks. Higher microstructural integrity in the fornix tail was found to be associated with significantly better recollection memory. In contrast, there was no significant correlation between fornix microstructure and familiarity memory or performance on two non-mnemonic tasks. Our findings support the idea that there are distinct MTL-diencephalon pathways that subserve differing memory processes.
PMCID: PMC2825810  PMID: 19940194
Recognition Memory; Fornix; Hippocampal function; Memory; Hippocampus; Imaging
6.  Can Complex Visual Discrimination Deficits in Amnesia Be Attributed to the Medial Temporal Lobe? An Investigation Into the Effects of Medial Temporal Lobe Damage on Brain Connectivity 
Hippocampus  2012;23(1):7-13.
It has been suggested that complex visual discrimination deficits in patients with medial temporal lobe (MTL) damage may be explained by damage or dysfunction beyond the MTL. We examined the resting functional networks and white matter connectivity of two amnesic patients who have consistently demonstrated discrimination impairments for complex object and/or spatial stimuli across a number of studies. Although exploratory analyses revealed some significant differences in comparison with neurologically healthy controls (more specifically in the patient with a larger MTL lesion), there were no obvious findings involving posterior occipital or posterior temporal regions, which can account entirely for their discrimination deficits. These findings converge with previous work to support the suggestion that the MTL does not subserve long-term declarative memory exclusively. © 2012 Wiley Periodicals, Inc.
PMCID: PMC3555392  PMID: 23233411
resting state networks; diffusion tensor imaging; MRI; hippocampus; perirhinal cortex

Results 1-6 (6)