Face-name association task reveals memory networks in patients with left and right hippocampal sclerosis

Investigating the effect of hippocampal sclerosis on parietal memory network

OBJECTIVE

We aimed to investigate differences in episodic memory networks between patients with temporal lobe epilepsy (TLE) due to hippocampal sclerosis and healthy controls, especially with regards to the parietal memory network (PMN), as well as their relation to neuropsychological memory performance after mesial temporal resection.

METHODS

28 healthy subjects as well as 21 patients with TLE (12 left, 9 right) were investigated using a spatial memory fMRI paradigm, which has been shown to activate the PMN. Regions of interest (ROI) were defined based on the results of the second-level analyses and activations within the predefined ROIs were compared across groups and correlated with postoperative verbal and nonverbal memory scores.

RESULTS

Healthy subjects showed activations within regions belonging to the dorsal visual stream and the PMN as well as the bilateral parahippocampal place area, the bilateral frontal eye field, and the bilateral middle frontal gyrus. Comparison between groups revealed that TLE patients activated significantly less in the left middle occipital gyrus and the right precuneus. The activation pattern in left TLE patients showed further reductions, mainly in areas belonging to the dorsal visual stream and the PMN within the left hemisphere. Activations within the left superior parietal lobulus, bilateral inferior parietal lobulus, bilateral middle temporal gyrus, left precuneus, left frontal eye field, and left middle frontal gyrus correlated significantly with postoperative verbal memory scores, and activations within the left superior parietal lobulus, left inferior parietal lobulus, left middle temporal gyrus, and left precuneus correlated significantly with higher performance in postoperative nonverbal memory scores.

SIGNIFICANCE

The PMN is involved in episodic memory encoding. Higher activations in areas belonging to the PMN and the dorsal visual stream, especially within the left hemisphere, before amygdalohippocampectomy may result in higher postoperative memory scores.

PLAIN LANGUAGE SUMMARY

This study aims to investigate the effects of epilepsy due to hippocampal sclerosis, i.e. scarring in the temporal lobe, on memory networks in the brain. We discovered that especially patients with left-sided hippocampal sclerosis show reduced brain activations in visual areas and memory networks within the left hemisphere of the brain during orientation in space. Importantly, higher activations within these areas may result in better memory after epilepsy surgery.

Structural and functional reorganization of contralateral hippocampus after temporal lobe epilepsy surgery

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Postoperative changes of contralateral hippocampus in temporal lobe epilepsy.

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No obvious hippocampal volume change was observed after successful surgery.

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Surgical manipulation may lead to a transient functional connectivity reduction.

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Increased functional connectivity mostly involved bilateral frontal regions.

Objective

To explore the structural and functional reorganization of contralateral hippocampus in patients with unilateral mesial temporal lobe epilepsy (mTLE) who achieved seizure-freedom after anterior temporal lobectomy (ATL).

Methods

We obtained high-resolution structural MRI and resting-state functional MRI data in 28 unilateral mTLE patients and 29 healthy controls. Patients were scanned before and three and 24 months after surgery while controls were scanned only once. Hippocampal gray matter volume (GMV) and functional connectivity (FC) were assessed.

Results

No obvious GMV changes were observed in contralateral hippocampus before and after successful surgery. Before surgery, ipsilateral hippocampus showed increased FC with ipsilateral insula (INS) and temporoparietal junction (TPJ), but decreased FC with widespread bilateral regions, as well as contralateral hippocampus. After successful ATL, contralateral hippocampus showed: (1) decreased FC with ipsilateral INS at three months follow-up, without further changes; (2) decreased FC with ipsilateral TPJ, postcentral gyrus and rolandic operculum at three months, with an obvious increase at 24 months follow-up; (3) increased FC with bilateral medial prefrontal cortex (MPFC) and superior frontal gyrus (SFG) at three months follow-up, without further changes.

Conclusions

Successful ATL may not lead to an obvious structural reorganization in contralateral hippocampus. Surgical manipulation may lead to a transient FC reduction of contralateral hippocampus. Increased FC between contralateral hippocampus and bilateral MPFC and SFG may be related to postoperative functional remodeling.

A Guide to Designing a Memory fMRI Paradigm for Pre-surgical Evaluation in Temporal Lobe Epilepsy

There has been increasing interest in the clinical and experimental use of memory functional Magnetic Resonance Imaging (fMRI). The 2017 American Academy of Neurology practice guidelines on the use of pre-surgical cognitive fMRI suggests that verbal memory fMRI could be used to lateralize memory functions in people with Temporal Lobe Epilepsy (TLE) and should be used to predict post-operative verbal memory outcome. There are however technical and methodological considerations, to optimize both the sensitivity and specificity of this imaging modality. Below we discuss these constraints and suggest recommendations to consider when designing a memory fMRI paradigm.

An fMRI Study of Adult Brain Cortical Activation Following Intensive Learning

Functional imaging techniques, fMRI in particular, has given the possibility to investigate non-invasively the cognitive processes in healthy populations and different disorders concerning neuro-psychiatry, thus unfolding the concepts guiding diagnosis and patient management. Different brain structures seem to support different types of cognitive functions in particular learning and memory thus the neurobiological explanation of the retrieval of information is associated with knowledge of brain plasticity, memory circuits, synaptic neurotransmission and the modulation of glial cells. Consistent with fMRI investigations of memory systems we tested the dependability of a memory paradigm using heterogeneous memory stimuli in order to find the neurobiological basis that correlates with memory task performance. Our study resulted with statistical significant differences in brain activations across the block design contrasts in both occipital and temporal regions in 29 mentally healthy students during a memory paradigm performance after intensive learning. As functional magnetic resonance imaging has become an important and reliable tool for investigation of brain anatomy and its function in health and disease, it becomes clear that further research of neurobiological basis of cognitive and memory domains can clarify different diagnostic prototypes and thus explain the human brain impairments in neuropsychological patients, since these are characterized by various cognitive dysfunctions.

Comparing the Wada Test and Functional MRI for the Presurgical Evaluation of Memory in Temporal Lobe Epilepsy

PURPOSE OF REVIEW

The usefulness of the Wada test (WT) predicting memory impairment from temporal lobe epilepsy (TLE) surgery has been debated, and it has progressively been replaced by functional MRI (fMRI). We review the current role of WT and fMRI in the presurgical assessment of TLE, and how novel surgical techniques might improve cognitive outcomes.

RECENT FINDINGS

fMRI's ability to predict global amnesia has not been assessed. Although WT can produce false-positive results, it is still indicated in patients at risk for developing global amnesia: those with significant bilateral or contralateral memory deficits. In the current review, WT exhibited no added value, beyond preclinical data, for predicting material-specific memory impairment, whereas fMRI was reliable for either verbal or non-verbal memory decline. Abnormal functional connectivity on resting state fMRI (rs-fMRI) between the posterior cingulate and the hippocampus may be a predictor of postsurgical memory outcomes. Restricted resections to the pathogenic tissue, stereotactic laser, radiosurgery, and SEEG-guided thermos-coagulation were associated with better cognitive outcome. fMRI should be used routinely in the presurgical workup of TLE to predict verbal and/or non-verbal memory decline, whereas WT may be indicated when there is a high risk of postsurgical global amnesia. Rs-fMRI is a promising tool for the presurgical workup of TLE, and more restricted resections are recommended to enhance cognitive outcomes.

Resting state functional connectivity and neural correlates of face-name encoding in patients with ischemic vascular lesions with and without the involvement of the left inferior frontal gyrus

Face-name association is a relevant ability for social interactions and involves the ventral and dorsolateral prefrontal cortices, particularly in the left hemisphere, bilateral hippocampal, fusiform gyrus and occipital regions. Previous studies demonstrated the primary role of the hippocampus for this ability in healthy subjects. However, no study has examined the participation of the left inferior frontal area, specially the left inferior frontal gyrus (LIFG) in patients with ischemic vascular lesions. In the present study we addressed this issue and investigated the neural correlates and resting state functional connectivity of face-name memory encoding in ischemic patients with LIFG or without lesions in the left IFG (nLIFG) and healthy controls (HC) using fMRI. The main results showed that the nLIFG group demonstrated efficient compensation related to encoding and performance on face-name learning and recognition memory task, in addition to similar brain areas activated during task performance compared to healthy controls. Some of these areas were more activated in nLIFG group, indicating a compensation mechanism. In contrast, the LIFG group showed worse behavior performance, and no signs of an efficient compensation mechanism. Functional connectivity analysis suggested that the left IFG region seems to be important for maintaining the connectivity of the right fusiform gyrus or, perhaps, lesion in this area is associated to maladaptive reorganization. Our findings highlight the relevant role of the left IFG in face-name learning and encoding, possibly as a primary region in addition to the bilateral hippocampal formation and fusiform gyrus.

Development of "material-specific" hemispheric specialization from beginning to end

Disparity of verbal and performance intelligence (VIQ, PIQ) on the Wechsler scales of intelligence is a conceptually cluttered and empirically weak measure of hemispheric specialization (HS). However, in the context of life span research, it is the only measure that can be exploited meta-analytically with the lesion method from prenatal life to late senescence. We assembled 1917 cases with a unilateral cortical focal brain lesion occurring at all ages and a post-lesion VIQ and PIQ. Lesion locus, volume and side were documented for each case, as well as age at lesion onset, age at first symptoms and age at the IQ test, presence/absence of epilepsy, lesion aetiology, gender, date of publication or of transfer of medical file. With and without covariate adjustment, HS was significant across the life span though its pattern changed. HS increased linearly and highly significantly until late senescence. Only in early adulthood did VIQ appear to vacate the right temporal lobe and occupy the left and PIQ vacate the left parietal lobe and occupy the right until late senescence. Biomaturational factors are more important in the ontogeny of material-specific HS over the whole life span than previously established.