Extratemporal functional connectivity impairments at rest are related to memory performance in mesial temporal epilepsy

Abstract

Mesial temporal lobe epilepsy (MTLE) is the most frequent form of focal epilepsy. At rest, there is evidence that brain abnormalities in MTLE are not limited to the epileptogenic region, but extend throughout the whole brain. It is also well established that MTLE patients suffer from episodic memory deficits. Thus, we investigated the relation between the functional connectivity seen at rest in fMRI and episodic memory impairments in MTLE. We focused on resting state BOLD activity and evaluated whether functional connectivity (FC) differences emerge from MTL seeds in left and right MTLE groups, compared with healthy controls. Results revealed significant FC reductions in both patient groups, localized in angular gyri, thalami, posterior cingulum and medial frontal cortex. We found that the FC between the left non-pathologic MTL and the medial frontal cortex was positively correlated with the delayed recall score of a non-verbal memory test in right MTLE patients, suggesting potential adaptive changes to preserve this memory function. In contrast, we observed a negative correlation between a verbal memory test and the FC between the left pathologic MTL and posterior cingulum in left MTLE patients, suggesting potential functional maladaptative changes in the pathologic hemisphere. Overall, the present study provides some indication that left MTLE may be more impairing than right MTLE patients to normative functional connectivity. Our data also indicates that the pattern of extra-temporal FC may vary as a function of episodic memory material and each hemisphere’s capacity for cognitive reorganization.

Frontal Lobe Epilepsy Alters Functional Connections Within the Brain's Motor Network: A Resting-State fMRI Study

“…association with impaired motor function (Widjaja et al, 2013). Our findings also extend upon previous studies of temporal lobe epilepsy patients, where reduced connectivity within memory networks was correlated with poorer memory test scores (Doucet et al, 2012), and decreased connectivity within language networks provided a possible explanation for patients' language impairments (Waites et al, 2006).…”

“…Altered connectivity has been reported in patients with neurological disorders, such as amyotrophic lateral sclerosis (Mohammadi et al, 2009), stroke (Park et al, 2011), Parkinson's disease (Wu et al, 2009), and multiple sclerosis (Dogonowski et al, 2013). In patients with left-hemisphere temporal lobe epilepsy, decreased connectivity has been demonstrated within language (Waites et al, 2006) and memory networks (Doucet et al, 2012), in association with language and memory deficits, respectively. This suggests that behavioral deficits in epilepsy may be the result of disrupted activity within associated resting-state networks, due to repeated seizure activity.…”

Hippocampal Atrophy Is Associated with Altered Hippocampus–Posterior Cingulate Cortex Connectivity in Mesial Temporal Lobe Epilepsy with Hippocampal Sclerosis

“…Our results are consistent with those of previous studies that reported decreased iFC between the PCC and the epileptogenic hippocampus or mesial temporal lobe in patients with left MTLEϩHS. 10,31 In addition, we observed increased iFC on the right side in the same group of patients (On-line Table). Bettus et al 32 investigated iFC between the hippocampus and other limbic structures on the healthy side in a group of patients with unilateral MTLE 32 ; they reported increased iFC between the right hippocampus and the right temporal pole and right amygdala in patients with left MTLE.…”

Network Construction and Graph Theoretical Analysis of Functional Language Networks in Pediatric Epilepsy

“…Controls tend to compartmentalize the brain into several smaller connected components as opposed to employing the whole brain to achieve a single language task. This decrease in efficiency agrees with other studies that demonstrated effects of epilepsy on memory networks (Campo et al, 2013;Vlooswijk et al, 2011;Voets et al, 2009), on resting state networks (Bettus et al, 2010;2009;Doucet et al, 2012;Liao et al, 2010a;Mankinen et al, 2012;Morgan et al, 2010;Waites et al, 2006;Z. Zhang et al, 2010), and on language networks Vlooswijk et al, 2010).…”