Neuroanatomical and psychological considerations in temporal lobe epilepsy

Abstract

Temporal lobe epilepsy (TLE) is the most common form of focal epilepsy and is associated with a variety of structural and psychological alterations. Recently, there has been renewed interest in using brain tissue resected during epilepsy surgery, in particular ‘non-epileptic’ brain samples with normal histology that can be found alongside epileptic tissue in the same epileptic patients — with the aim being to study the normal human brain organization using a variety of methods. An important limitation is that different medical characteristics of the patients may modify the brain tissue. Thus, to better determine how ‘normal’ the resected tissue is, it is fundamental to know certain clinical, anatomical and psychological characteristics of the patients. Unfortunately, this information is frequently not fully available for the patient from which the resected tissue has been obtained — or is not fully appreciated by the neuroscientists analyzing the brain samples, who are not necessarily experts in epilepsy. In order to present the full picture of TLE in a way that would be accessible to multiple communities (e.g., basic researchers in neuroscience, neurologists, neurosurgeons and psychologists), we have reviewed 34 TLE patients, who were selected due to the availability of detailed clinical, anatomical, and psychological information for each of the patients. Our aim was to convey the full complexity of the disorder, its putative anatomical substrates, and the wide range of individual variability, with a view toward: (1) emphasizing the importance of considering critical patient information when using brain samples for basic research and (2) gaining a better understanding of normal and abnormal brain functioning. In agreement with a large number of previous reports, this study (1) reinforces the notion of substantial individual variability among epileptic patients, and (2) highlights the common but overlooked psychopathological alterations that occur even in patients who become “seizure-free” after surgery. The first point is based on pre- and post-surgical comparisons of patients with hippocampal sclerosis and patients with normal-looking hippocampus in neuropsychological evaluations. The second emerges from our extensive battery of personality and projective tests, in a two-way comparison of these two types of patients with regard to pre- and post-surgical performance.

Chronic Epilepsy and Mossy Fiber Sprouting Following Organophosphate-Induced Status Epilepticus in Rats

“…Human and animal data also indicate hilar cell loss following SE and epilepsy ( Covolan and Mello, 2000 ; Rojas et al, 2021 ; DeFelipe et al, 2022 ). Our findings suggest that following OP-induced SE, in the chronic phase, hilar neuronal loss was not necessarily indicative of the development of epilepsy.…”

Ultrastructural sublaminar-specific diversity of excitatory synaptic boutons in layer 1 of the adult human temporal lobe neocortex

“…Synaptic density measurement are a useful tool to describe the synaptic organization of a particular area, nuclei and even layers in different brain regions, but also the degree of connectivity underlying the computational properties of a given brain area or in a given brain network. Meanwhile numerous studies in various animal species and brain regions have performed such an analysis but data for a density of synaptic complexes in humans are still rare (but see Marco and DeFelipe 1998; Tang et al 2001; DeFelipe et al 1999, 2002; Alonso-Nanclares et al 2008; Blazquez-Llorca et al 2013; Finnema et al 2016; Cano-Astorga et al 2021, 2023).…”

Comparison of spontaneous recurrent seizures in rats following status epilepticus induced by organophosphate paraoxon, DFP, and sarin

“…MFS (Franck et al, 1995;Proper et al, 2000;Buckmaster et al, 2002;Buckmaster, 2014) and cell loss in the hilus region of the dentate gyrus (Covolan and Mello, 2000;Rojas et al, 2021;DeFelipe et al, 2022) is reported in both human epilepsy and animal models of epilepsy. Following SE, hippocampal mossy fibers of dentate granule cells are said to develop recurrent collaterals that invade the dentate IML to generate recurrent excitation by forming granule cell-granule cell synapses (Mello et al, 1993;Okazaki et al, 1995).…”