Medial temporal lobe regions mediate complex visual discriminations for both objects and scenes: A process-based view

Contribution of the lateral occipital and parahippocampal cortices to pattern separation of objects and contexts

Contextual features are integral to episodic memories; yet, we know little about context effects on pattern separation, a hippocampal function promoting orthogonalization of overlapping memory representations. Recent studies suggested that various extrahippocampal brain regions support pattern separation; however, the specific role of the parahippocampal cortex-a region involved in context representation-in pattern separation has not yet been studied. Here, we investigated the contribution of the parahippocampal cortex (specifically, the parahippocampal place area) to context reinstatement effects on mnemonic discrimination, using functional magnetic resonance imaging. During scanning, participants saw object images on unique context scenes, followed by a recognition task involving the repetitions of encoded objects or visually similar lures on either their original context or a lure context. Context reinstatement at retrieval improved item recognition but hindered mnemonic discrimination. Crucially, our region of interest analyses of the parahippocampal place area and an object-selective visual area, the lateral occipital cortex indicated that while during successful mnemonic decisions parahippocampal place area activity decreased for old contexts compared to lure contexts irrespective of object novelty, lateral occipital cortex activity differentiated between old and lure objects exclusively. These results imply that pattern separation of contextual and item-specific memory features may be differentially aided by scene and object-selective cortical areas.

Altered dynamic and static brain activity and functional connectivity in COVID-19 patients: a preliminary study

This study aimed to investigate the effects of COVID-19 on brain functional activity through resting-state functional MRI (rs-fMRI). fMRI scans were conducted on a cohort of 42 confirmed COVID-19-positive patients and 46 healthy controls (HCs) to assess brain functional activity. A combination of dynamic and static amplitude of low-frequency fluctuations (dALFF/sALFF) and dynamic and static functional connectivity (dFC/sFC) was used for evaluation. Abnormal brain regions identified were then used as feature inputs in the model to evaluate support vector machine (SVM) capability in recognizing COVID-19 patients. Moreover, the random forest (RF) model was employed to verify the stability of SVM diagnoses for COVID-19 patients. Compared to HCs, COVID-19 patients exhibited a decrease in sALFF in the right lingual gyrus and the left medial occipital gyrus and an increase in dALFF in the right straight gyrus. Moreover, there was a decline in sFC between both lingual gyri and the right superior occipital gyrus and a reduction in dFC with the precentral gyrus. The dynamic and static combined ALFF and FC could distinguish between COVID-19 patients and the HCs with an accuracy of 0.885, a specificity of 0.818, a sensitivity of 0.933 and an area under the curve of 0.909. The combination of dynamic and static ALFF and FC can provide information for detecting brain functional abnormalities in COVID-19 patients.

Complex visual discrimination is impaired after right, but not left, anterior temporal lobectomy

The prevailing view in human cognitive neuroscience associates the medial temporal lobes (MTLs) with declarative memory. Compelling experimental evidence has, however, demonstrated that these regions are specialized according to the representations processed, irrespective of the cognitive domain assessed. This account was supported by the study of patients with bilateral medial temporal amnesia, who exhibit impairments in perceptual tasks involving complex visual stimuli. Yet, little is known regarding the impact of unilateral MTL damage on complex visual abilities. To address this issue, we administered a visual matching task to 20 patients who underwent left (N = 12) or right (N = 8) anterior temporal lobectomy for drug-resistant epilepsy and to 38 healthy controls. Presentation viewpoint was manipulated to increase feature ambiguity, as this is critical to reveal impairments in perceptual tasks. Similar to control participants, patients with left-sided damage succeeded in all task conditions. In contrast, patients with right-sided damage had decreased accuracy compared with that of the other two groups, as well as increased response time. Notably, the accuracy of those with right-sided damage did not exceed chance level when feature ambiguity was high (i.e., when stimuli were presented from different viewpoints) for the most complex classes of stimuli (i.e., scenes and buildings, compared with single objects). The pattern reported in bilateral patients in previous studies was therefore reproduced in patients with right, but not left, resection. These results suggest that the complex visual-representation functions supported by the MTL are right-lateralized, and raise the question as to how the representational account of these regions applies to representations supported by left MTL regions.

Patterns of Impaired Neurocognitive Performance on the Global Neuropsychological Assessment, and Their Brain Structural Correlates in Recent-onset and Chronic Schizophrenia

Objective

Schizophrenia is associated with impairment in multiple cognitive domains. There is a paucity of research on the effect of prolonged illness duration (≥ 15 years) on cognitive performance along multiple domains. In this pilot study, we used the Global Neuropsychological Assessment (GNA), a brief cognitive battery, to explore the patterns of cognitive impairment in recent-onset (≤ 2 years) compared to chronic schizophrenia (≥ 15 years), and correlate cognitive performance with brain morphometry in patients and healthy adults.

Methods

We assessed cognitive performance in patients with recent-onset (n = 17, illness duration ≤ 2 years) and chronic schizophrenia (n = 14, duration ≥ 15 years), and healthy adults (n = 16) using the GNA and examined correlations between cognitive scores and gray matter volumes computed from T1-weighted magnetic resonance imaging images.

Results

We observed cognitive deficits affecting multiple domains in the schizophrenia samples. Selectively greater impairment of perceptual comparison speed was found in adults with chronic schizophrenia (p = 0.009, η2partial = 0.25). In the full sample (n = 47), perceptual comparison speed correlated significantly with gray matter volumes in the anterior and medial temporal lobes (TFCE, FWE p < 0.01).

Conclusion

Along with generalized deficit across multiple cognitive domains, selectively greater impairment of perceptual comparison speed appears to characterize chronic schizophrenia. This pattern might indicate an accelerated or premature cognitive aging. Anterior-medial temporal gray matter volumes especially of the left hemisphere might underlie the impairment noted in this domain in schizophrenia.

Familiarity Deficits for Words and Objects in Amnestic Mild Cognitive Impairment in a Context Minimizing the Role of Recollection

OBJECTIVES

Amnestic mild cognitive impairment (aMCI) is associated with cortical thinning in perirhinal and entorhinal cortices, key regions of the brain supporting familiarity. Individuals with aMCI demonstrate familiarity deficits in their behavior, often repeating questions in the same conversation. While familiarity deficits in healthy aging are minimal, past studies measuring familiarity in aMCI have mixed results, perhaps due to the influence of recollection. We therefore used a paradigm that minimized the influence of recollection, and hypothesized that familiarity would be impaired in aMCI relative to age-matched controls, but not in healthy older adults relative to younger adults. We also hypothesized that familiarity deficits in aMCI would be greater for objects than words because the perirhinal cortex plays a significant role in visual discrimination.

METHODS

A sample of 36 younger adults, 38 cognitively intact older adults, and 30 older adults with aMCI made absolute frequency judgments for words and objects seen a variable number of times in an incidental encoding task. Estimates of familiarity were derived from correlating participants' frequency judgments with the actual frequency of presentation.

RESULTS

Familiarity was largely spared in healthy aging, with minor deficits in familiarity for words. Familiarity deficits were evident in aMCI comparably for words and objects.

DISCUSSION

The present research underscores the need to study familiarity in contexts minimizing recollection, particularly when comparing groups with different levels of recollection, and adds to our understanding of the phenomenology of aMCI. Familiarity deficits may provide an early biomarker of dementia risk.

Hippocampal activity during memory and visual perception: The role of representational content

The functional organisation of the medial temporal lobe (MTL) has long been described on the basis of cognitive processes such as recollection or familiarity. However, this view has recently been challenged, and researchers have proposed decomposing cognitive phenomena into representations and operations. According to the representational view, representations, such as scenes for the hippocampus and objects for the perirhinal cortex, are critical in understanding the role of MTL regions in cognition. In the present study, 51 healthy young participants underwent functional magnetic resonance imaging (fMRI) while completing a visual-discrimination task. Subsequently, half of the participants performed a patch-cue recognition procedure in which "Rec" responses are believed to reflect the operation of pattern completion, whereas the other half performed a whole-item remember/know procedure. We replicated the previously-reported demonstration that hippocampal involvement in pattern completion is preferential for scenes as compared with objects. In contrast, the perirhinal cortex was more recruited for object processing than for scene processing. We further extended these results to the operations of strength-signal memory and visual discrimination. Finally, the modulation of hippocampal engagement in pattern completion by representational content was found to be specific to its anterior segment. This observation is consistent with the proposal that this segment would process broad/global representations, whereas the posterior hippocampus would perform sharp/local representations. Taken together, these results favour the representational view of MTL functional organisation, but support that this specialisation differs along the hippocampal long-axis.

Category-sensitive incidental reinstatement in medial temporal lobe subregions during word recognition

During associative retrieval, the brain reinstates neural representations that were present during encoding. The human medial temporal lobe (MTL), with its subregions hippocampus (HC), perirhinal cortex (PRC), and parahippocampal cortex (PHC), plays a central role in neural reinstatement. Previous studies have given compelling evidence for reinstatement in the MTL during explicitly instructed associative retrieval. High-confident recognition may be similarly accompanied by recollection of associated information from the encoding context. It is unclear, however, whether high-confident recognition memory elicits reinstatement in the MTL even in the absence of an explicit instruction to retrieve associated information. Here, we addressed this open question using high-resolution fMRI. Twenty-eight male and female human volunteers engaged in a recognition memory task for words that they had previously encoded together with faces and scenes. Using complementary univariate and multivariate approaches, we show that MTL subregions including the PRC, PHC, and HC differentially reinstate category-sensitive representations during high-confident word recognition, even though no explicit instruction to retrieve the associated category was given. This constitutes novel evidence that high-confident recognition memory is accompanied by incidental reinstatement of associated category information in MTL subregions, and supports a functional model of the MTL that emphasizes content-sensitive representations during both encoding and retrieval.

Perirhinal and Postrhinal Damage Have Different Consequences on Attention as Assessed in the Five-Choice Serial Reaction Time Task

The perirhinal (PER) and postrhinal (POR) cortices, structures in the medial temporal lobe, are implicated in learning and memory. The PER is understood to process object information and the POR to process spatial or contextual information. Whether the medial temporal lobe is dedicated to memory, however, is under debate. In this study, we addressed the hypothesis that the PER and POR are also involved in non-mnemonic cognitive functions. Rats with PER or POR damage and SHAM surgical controls were shaped, trained, and tested on the five-choice serial reaction time (5CSRT) task, which assesses attention and executive function. Rats with PER damage were impaired in acquiring the task and at asymptote, although processing information about objects was not relevant to the task. When confronted with attentional challenges, rats with PER damage showed a pattern consistent with decreased attentional capacity, increased response errors, and increased impulsive behavior. Rats with POR damage showed intact acquisition and normal asymptotic performance. They also exhibited faster latencies in the absence of speed accuracy trade-off suggesting enhanced response readiness. We suggest this increased response readiness results from decreased automatic monitoring of the local environment, which might normally compete with response readiness. Our findings are consistent with a role for PER in controlled attention and a role for POR in stimulus-driven attention providing evidence that the PER and POR cortices have functions that go beyond memory for objects and memory for scenes and contexts, respectively. These findings provide new evidence for functional specialization in the medial temporal lobe.