Brain plasticity for verbal and visual memories in patients with mesial temporal lobe epilepsy and hippocampal sclerosis: An fMRI study

Abstract

We aimed to identify the brain areas involved in verbal and visual memory processing in normal controls and patients with unilateral mesial temporal lobe epilepsy (MTLE) associated with unilateral hippocampal sclerosis (HS) by means of functional magnetic resonance imaging (fMRI). The sample comprised nine normal controls, eight patients with right MTLE, and nine patients with left MTLE. All subjects underwent fMRI with verbal and visual memory paradigms, consisting of encoding and immediate recall of 17 abstract words and 17 abstract drawings. A complex network including parietal, temporal, and frontal cortices seems to be involved in verbal memory encoding and retrieval in normal controls. Although similar areas of activation were identified in both patient groups, the extension of such activations was larger in the left-HS group. Patients with left HS also tended to exhibit more bilateral or right lateralized encoding related activations. This finding suggests a functional reorganization of verbal memory processing areas in these patients due to the failure of left MTL system. As regards visual memory encoding and retrieval, our findings support the hypothesis of a more diffuse and bilateral representation of this cognitive function in the brain. Compared to normal controls, encoding in the left-HS group recruited more widespread cortical areas, which were even more widespread in the right-HS group probably to compensate for their right mesial temporal dysfunction. In contrast, the right-HS group exhibited fewer activated areas during immediate recall than the other two groups, probably related to their greater difficulty in dealing with visual memory content.

Five-Year Neuropsychological Outcome after Stereotactic Radiofrequency Amygdalohippocampectomy for Mesial Temporal Lobe Epilepsy: Longitudinal Study

“…Both of these approaches have the potential for reorganization of temporal or extratemporal networks supporting cognitive functions. Preferentially, nonlesional approaches are especially promising in terms of specific mesial temporal lobe-related memory functions, for example, encoding [39,40]. …”

Applications of Blood-Oxygen-Level-Dependent Functional Magnetic Resonance Imaging and Diffusion Tensor Imaging in Epilepsy

“…Lateralization of visual memory encoding to the contralateral hemisphere is associated with decreased and increased verbal memory performance in patients with left and right TLE, respectively. 82,88,89 Greater right hippocampal activation for face encoding is correlated with better visual memory in patients with right TLE. 84,86 Functional connectivity is reduced between the posterior cingulate and the epileptogenic hippocampus and increased between the posterior cingulate and the contralateral hippocampus.…”

“…80,81 Episodic memory-related networks Verbal memory encoding recruits a bilateral network, including parietal, temporal, and frontal cortices, lateralized to the hemisphere contralateral to the epileptic focus, in patients with TLE. 82,83 Greater left hippocampal activation for word encoding is correlated with better verbal memory in patients with left TLE. [84][85][86] Frontal lobe involvement is more bilateral in left TLE and lateralized in right TLE.…”

“…90 Verbal and visual memory immediate recall shows less activation in patients with HS compared with controls. 82 Patients tend to use the opposite hippocampus and parahippocampal gyrus on the same side, suggesting adaptation or functional reorganization. 92 Working memory-related networks Working memory is also affected in patients with TLE with HS, showing variable connectivity between brain regions.…”

Third International Congress on Epilepsy, Brain, and Mind: Part 2

“…Based on empirical data and recent literature on the significant reorganization of speech and memory in patients with left-sided MTLE/HS, we tested the hypothesis that left-sided MTLE/HS has a significant impact on the organization of motor cortex and handedness [76][77][78][79][80][81][82]. To investigate hand dominance in subgroups of patients with right-and left-sided MTLE/HS, 73 subjects with a diagnosis of unilateral MTLE/HS were prospectively included in the analysis.…”