Cerebellar pathology does not impair performance on identification or categorization tasks.

Eye movement strategies in face ethnicity categorization vs. face identification tasks

The way in which we respond to everyday stressors can have a profound impact on cognitive functioning. Maladaptive stress responses in particular are generally associated with impaired cognitive performance. We argue, however, that the cognitive system mediating task performance is also a critical determinant of the stress-cognition relationship. Consistent with this prediction, we observed that stress reactivity consistent with a maladaptive, threat response differentially predicted performance on two categorization tasks. Increased threat reactivity predicted enhanced performance on an information-integration task (i.e., learning is thought to depend upon a procedural-based memory system), and a (nonsignificant) trend for impaired performance on a rule-based task (i.e., learning is thought to depend upon a hypothesis-testing system). These data suggest that it is critical to consider both variability in the stress response and variability in the cognitive system mediating task performance in order to fully understand the stress-cognition relationship.

Imaging of Eating Disorders: Multiple Techniques to Demonstrate the Dynamic Brain

The ability to group items and events into functional categories is a fundamental function for visual recognition. Experimental studies have shown the different roles in information representations of inferior temporal (IT) and prefrontal cortices (PFC) in a categorization task. However, it remains elusive how category information is generated in PFC and maintained in a delay period and how the interaction between IT and PFC influences category performance. To address these issues, we develop a network model of visual system, which performs a delayed match-to-category task. The model consists of networks of V4, IT, and PFC. We show that in IT visual information required for categorization is represented by a combination of prototype features. We also show that category information in PFC is represented by two dynamical attractors weakly linked, resulting from the difference in firing thresholds of PFC neurons. Lower and higher firing thresholds contribute to working memory maintenance and decision-making, respectively. Furthermore, we show that top-down signal from PFC to IT improves the ability of PFC neurons to categorize the mixed images that are closer to a category boundary. Our model may provide a clue for understanding the neural mechanism underlying categorization task.

The present study compared four different structural magnetic resonance imaging (MRI) techniques used to measure gray matter atrophy in Alzheimer's disease (AD): manual and automated volumetry, cortical thickness (CT) and voxel-based morphometry (VBM)). These techniques are used interchangeably in AD research and thus far it is unclear which technique is superior in detecting abnormalities early in the disease process. We inquired whether these techniques show similar results in healthy controls (con), patients with amnestic mild cognitive impairment (MCI) and patients suffering from mild AD. In addition, we investigated whether atrophy of prefrontal cortex (PFC) or medial temporal lobe (MTL) regions is most indicative of (preclinical) AD. Three groups of older male participants were selected: 18 healthy participants without any memory impairment, 18 patients with amnestic MCI, and 18 patients with mild AD. Between-group differences were investigated in PFC and MTL regions. A manual and automatic tracing approach were applied to calculate gray matter volume. CT was furthermore calculated by Freesurfer as the average thickness of the cortical surface in each ROI. VBM was applied by using masks of atlas-based ROI's in FSL. Manually measured right parahippocampal gyrus (PHG) volumes can differentiate con and MCI. Con and AD can furthermore be distinguished by manually measured hippocampus and PHG volumes, and by automated measurements of hippocampus and entorhinal cortex (ERC). Manual segmentation techniques are also sensitive for changes in PFC areas showing abnormalities in inferior and orbital PFC (con /AD and MCI/AD). CT analysis showed differences between con and AD in ERC, right inferior prefrontal (IPFC) and left medial orbitofrontal cortex (OFC) regions. VBM-ROI analyses showed differences between con/AD and MCI/AD in hippocampus, IPFC and OPFC (Table 1). The present study demonstrates that manual volumetry and VBM are able to detect group differences in both PFC and MTL structures (con/AD and MCI/AD). Manual volumetry of the right PhG can furthermore differentiate between con and MCI. The present study confirms earlier theories that the MTL is most indicative of (preclinical) AD, showing abnormalities in all the investigated techniques.

The effects of lesions of superior temporal gyrus and inferior parietal lobe on temporal and vertex components of the human AEP

Objective Cushing's syndrome is associated with long-term cognitive deficits and affective symptoms such as depression and anxiety. The alterations in brain function underlying these deficits after Cushing's syndrome are unclear and therefore we aimed to explore alterations in resting-state functional connectivity in patients with Cushing's syndrome in remission. Design Cross-sectional case-control study. Methods Nineteen women with Cushing's syndrome in remission for a median time of 7 years (IQR: 6-10) and a mean age of 45 years were included at three university clinics. These patients and 38 age-matched female controls underwent brain imaging at a single center. The main outcome measure was functional connectivity at rest, measured with functional magnetic resonance imaging. Results The medial temporal lobe (MTL) and prefrontal cortex networks, exhibited elevated functional connectivity among patients compared to controls. The degree of elevated functional connectivity in the MTL was negatively associated with time in remission. Conclusions Resting-state functional connectivity within glucocorticoid receptor-rich regions, particularly the MTL and medial prefrontal cortex, was increased in patients. These differences in connectivity may provide a neural basis for the cognitive deficits and affective symptoms commonly experienced by patients with Cushing's syndrome in remission.

Electrical stimulation of the medial temporal lobe (MTL) has the potential to uncover causal circuit mechanisms underlying memory function. However, little is known about how MTL stimulation alters information flow with frontoparietal cortical regions implicated in episodic memory. We used intracranial EEG recordings from humans (14 participants, 10 females) to investigate how MTL stimulation alters directed information flow between MTL and PFC and between MTL and posterior parietal cortex (PPC). Participants performed a verbal episodic memory task during which they were presented with words and asked to recall them after a delay of ∼20 s; 50 Hz stimulation was applied to MTL electrodes on selected trials during memory encoding. Directed information flow was examined using phase transfer entropy. Behaviorally, we observed that MTL stimulation reduced memory recall. MTL stimulation decreased top-down PFC→MTL directed information flow during both memory encoding and subsequent memory recall, revealing aftereffects more than 20 s after end of stimulation. Stimulation suppressed top-down PFC→MTL influences to a greater extent than PPC→MTL. Finally, MTL→PFC information flow on stimulation trials was significantly lower for successful, compared with unsuccessful, memory recall; in contrast, MTL→ventral PPC information flow was higher for successful, compared with unsuccessful, memory recall. Together, these results demonstrate that the effects of MTL stimulation are behaviorally, regionally, and directionally specific, that MTL stimulation selectively impairs directional signaling with PFC, and that causal MTL-ventral PPC circuits support successful memory recall. Findings provide new insights into dynamic casual circuits underling episodic memory and their modulation by MTL stimulation.SIGNIFICANCE STATEMENT The medial temporal lobe (MTL) and its interactions with prefrontal and parietal cortices (PFC and PPC) play a critical role in human memory. Dysfunctional MTL-PFC and MTL-PPC circuits are prominent in psychiatric and neurologic disorders, including Alzheimer's disease and schizophrenia. Brain stimulation has emerged as a potential mechanism for enhancing memory and cognitive functions, but the underlying neurophysiological mechanisms and dynamic causal circuitry underlying bottom-up and top-down signaling involving the MTL are unknown. Here, we use intracranial EEG recordings to investigate the effects of MTL stimulation on causal signaling in key episodic memory circuits linking the MTL with PFC and PPC. Our findings have implications for translational applications aimed at realizing the promise of brain stimulation-based treatment of memory disorders.

From sensorimotor learning to memory cells in prefrontal and temporal association cortex: A neurocomputational study of disembodiment

Last year, we showed that most of the visual processing for categorising centrally presented images could be done in 150 ms. The human subjects were given a go — no go categorisation task in which they had to release a button when they could identify an animal. All the pictures were natural scenes taken from a vast CD-ROM data bank allowing access to several thousands of stimuli so that each image was only seen once. Targets (animals) included fish, birds, mammals, reptiles, insects in their natural environment; distractors included landscapes, trees, flowers, fruits. They were presented for a very short duration (20 ms) in order to avoid eye movement. In the present study we wanted to evaluate how the performance was affected with extrafoveal stimulations. We used the same task, but the visual stimuli could be presented at random, either centrally where subjects had to maintain fixation or laterally (left or right hemifield). Behavioural data and concomitant evoked potentials were recorded. The subject's performance was extremely good with a mean score of 90% correct and a mean reaction time of 500 ms. Comparison of performance between central and lateral stimulations showed that most subjects could process lateral and central stimuli with the same speed (reaction time distributions were not statistically different), and that, although extrafoveal presentations induced a drop in the percentage of correct responses (mean decrease 5%), it was not significant in all subjects. Moreover, when compared with last year's study the increase of the number of spatial locations where the visual stimulus could appear did not induce a significant behavioural cost, in terms of speed or accuracy of the response. We also looked at a possible hemispheric specialisation with no clear results. The results obtained here show that even with shared spatial attention and extrafoveal vision, the human visual system is remarkably efficient in an identification task.

Category number effects on rule-based and information-integration category learning were investigated. Category number affected accuracy and the distribution of best-fitting models in the rule-based task but had no effect on accuracy and little effect on the distribution of best-fining models in the information-integration task. In the 2 category conditions, rule-based learning was better than information-integration learning, whereas in the 4 category conditions, unidimensional and conjunctive rule-based learning was worse than information-integration learning. Rule-based strategies were used in the 2-category/rule-based condition, but about half of the observers used rule-based strategies in the 4-category unidimensional and conjunctive rule-based conditions. Information-integration strategies were used in the 4-category/ information-integration condition and by the end of training were used in the 2-category/information-integration condition.

Goal-directed visual attention is a fundamental cognitive process that enables animals to selectively focus on specific regions of the visual field while filtering out irrelevant information. However, given the domain specificity of social behaviors, it remains unclear whether attention to faces versus nonfaces recruits different neurocognitive processes. In this study, we simultaneously recorded activity from temporal and frontal nodes of the attention network while macaques performed a goal-directed visual search task. V4 and inferotemporal (IT) visual category-selective units, selected during cue presentation, discriminated fixations on targets and distractors during the search but were differentially engaged by face and house targets. V4 and IT category-selective units also encoded fixation transitions and search dynamics. Compared with distractors, fixations on targets reduced spike-LFP coherence within the temporal cortex. Importantly, target-induced desynchronization between the temporal and prefrontal cortices was only evident for face targets, suggesting that attention to faces differentially engaged the prefrontal cortex. We further revealed bidirectional theta influence between the temporal and prefrontal cortices using Granger causality, which was again disproportionate for faces. Finally, we showed that the search became more efficient with increasing target-induced desynchronization. Together, our results suggest domain specificity for attending to faces and an intricate interplay between visual attention and social processing neural networks.

Categorization is our ability to generalize properties of object, and clearly fundamental cognitive capacity. A delayed match-to-categorization task requires working memory of category information, shaped by the interaction between prefrontal cortex (PFC) and inferior temporal (IT) cortex. In the present study, we present the neural mechanism by which working memory is shaped and retained in PFC and how top-down signals from PFC to IT affect the categorization ability.

Differential roles for medial prefrontal and medial temporal cortices in schema-dependent encoding: From congruent to incongruent

There is substantial overlap between the brain regions supporting episodic memory and the default network. However, in humans, the impact of bilateral medial temporal lobe (MTL) damage on a large-scale neural network such as the default mode network is unknown. To examine this issue, resting fMRI was performed with amnesic patients and control participants. Seed-based functional connectivity analyses revealed robust default network connectivity in amnesia in cortical default network regions such as medial prefrontal cortex, posterior medial cortex, and lateral parietal cortex, as well as evidence of connectivity to residual MTL tissue. Relative to control participants, decreased posterior cingulate cortex connectivity to MTL and increased connectivity to cortical default network regions including lateral parietal and medial prefrontal cortex were observed in amnesic patients. In contrast, somatomotor network connectivity was intact in amnesic patients, indicating that bilateral MTL lesions may selectively impact the default network. Changes in default network connectivity in amnesia were largely restricted to the MTL subsystem, providing preliminary support from MTL amnesic patients that the default network can be fractionated into functionally and structurally distinct components. To our knowledge, this is the first examination of the default network in amnesia.