Multimodal P3 under different attentional states in mesial temporal lobe epilepsy

Resting state network dynamic reconfiguration and neuropsychological functioning in temporal lobe epilepsy: An HD-EEG investigation

Temporal lobe epilepsy (TLE) is nowadays considered a network disorder impacting several cognitive domains. In this work we investigated dynamic network reconfiguration differences in patients with unilateral TLE compared to a healthy control group, focusing on two connectivity indices: flexibility and integration. We apply these indices for the first time to high-density EEG source-based functional connectivity. We observed that patients with TLE exhibited significantly lower flexibility than healthy controls in the Control, Default Mode and Attentive Dorsal networks, expressed in the delta, theta and alpha bands. In addition, patients with TLE displayed greater integration values across the majority of the resting state networks, especially in the delta, theta and gamma bands. Relevantly, a higher integration index in the Control, Attentive Dorsal and Visual networks in the delta band was correlated with lower performance in visual attention and executive functions. Moreover, a greater integration index in the gamma band of the Control, Somatomotor and Temporoparietal networks was related to lower long-term memory performance. These results suggest that patients with TLE display dysregulated network reconfiguration, with lower flexibility in the brain areas related to cognitive control and attention, together with excessive inter-network communication (integration index). Finally, the correlation between network integration and the reduced cognitive performance suggests a potential mechanism underlying specific alterations in neuropsychological profile of patients with TLE.

Monaural 40-Hz auditory steady-state magnetic responses can be useful for identifying epileptic focus in mesial temporal lobe epilepsy

OBJECTIVE

Patients with mesial temporal lobe epilepsy (mTLE) often exhibit central auditory processing (CAP) dysfunction. Monaural 40-Hz auditory steady-state magnetic responses (ASSRs) were recorded to explore the pathophysiology of mTLE.

METHODS

Eighteen left mTLE patients, 11 right mTLE patients and 16 healthy controls (HCs) were examined. Monaural clicks were presented at a rate of 40 Hz. Phase-locking factor (PLF) and power values were analyzed within bilateral Heschl's gyri.

RESULTS

Monaural 40-Hz ASSR demonstrated temporal frequency dynamics in both PLF and power data. Symmetrical hemispheric contralaterality was revealed in HCs. However, predominant contralaterality was absent in mTLE patients. Specifically, right mTLE patients exhibited a lack of contralaterality in response to left ear but not right ear stimulation, and vice versa in left mTLE patients.

CONCLUSION

This is the first study to use monaural 40-Hz ASSR with unilateral mTLE patients to clarify the relationship between CAP and epileptic focus. CAP dysfunction was characterized by a lack of contralaterality corresponding to epileptic focus.

SIGNIFICANCE

Monaural 40-Hz ASSR can provide useful information for localizing epileptic focus in mTLE patients.

Temporal resolution in individuals with neurological disorders

OBJECTIVE

Temporal processing refers to the ability of the central auditory nervous system to encode and detect subtle changes in acoustic signals. This study aims to investigate the temporal resolution ability of individuals with mesial temporal sclerosis and to determine the sensitivity and specificity of the gaps-in-noise test in identifying this type of lesion.

METHOD

This prospective study investigated differences in temporal resolution between 30 individuals with normal hearing and without neurological lesions (G1) and 16 individuals with both normal hearing and mesial temporal sclerosis (G2). Test performances were compared, and the sensitivity and specificity were calculated.

RESULTS

There was no difference in gap detection thresholds between the two groups, although G1 revealed better average thresholds than G2 did. The sensitivity and specificity of the gaps-in-noise test for neurological lesions were 68% and 98%, respectively.

CONCLUSIONS

Temporal resolution ability is compromised in individuals with neurological lesions caused by mesial temporal sclerosis. The gaps-in-noise test was shown to be a sensitive and specific measure of central auditory dysfunction in these patients.

Impaired perceptual networks in temporal lobe epilepsy revealed by resting fMRI

Viewed as a neural network disorder, mesial temporal lobe epilepsy (mTLE) may cause widespread deficits in human brain functions. Impairments in cognitive functions such as memory and language have been well addressed, but perceptual deficits have only been considered in terms of behavioral data. Little imaging research on perceptual deficits in mTLE has been reported. The present study is expected to reveal impairments in the perceptual networks in patients with mTLE using fMRI. The fMRI-based independent component analysis (ICA) was applied to 33 patients with mTLE and 33 matched healthy controls. In light of the resting-state networks (RSNs) corresponding to the basal functions of visual, auditory, and sensorimotor systems, the ICA data of functional connectivity within these RSNs were compared between the patients and controls. Compared with the controls, the mTLE patients presented decreased functional connectivity within the regions of the auditory and sensorimotor networks, as well increased functional connectivity in the primary visual cortex and decreased functional connectivity in the bilateral MT+ areas of the visual network. Our neuroimaging results are in agreement with the previous findings that specific perceptual functions are impaired in mTLE. Furthermore, our findings in the visual network support the belief that the primary visual function is not impaired and that there may be deficits in the high-order visual function in mTLE. Our fMRI study may contribute to the understanding of neuropathophysiological mechanisms underlying perceptual impairments in mTLE.

Attention changes in epilepsy patients following 3-month topiramate or valproate treatment revealed by event-related potential

The present study was designed to reveal changes of cognitive processes in epilepsy (EP) patients with Topiramate (TPM) or Valproate (VPA) treatment using Wechsler Adult Intelligence Scale (WAIS-CR) and event-related potential (ERP). Thirty untreated epilepsy patients were randomly divided into two groups receiving TPM or VPA, respectively. Fifteen healthy volunteers were included as controls. All the patients were examined by WAIS-CR and ERP before and 3 months after drug treatment. Controls were examined by ERP at the time recruited into the study and 3 months later. Unfamiliar grey-scale photographs of faces (front view) were used as stimuli. ERP were recorded at the same time. Mean Intelligence Quotient (IQ) in TPM group decreased after the 3-month treatment (90.40 vs. 81.00, P<0.05). One component of ERP-P300 was smaller in epilepsy patients than controls (P<0.05), but remained unchanged after TPM or VPA treatment (P>0.05). A delayed and smaller N270 was detected in patients compared to controls (P<0.05). After 3 months TPM treatment, it decreased further compared to before treatment (P<0.05). N170 was lower in patient groups, and it became lower after TPM treatment than before. Our results demonstrate that in all epilepsy patients with mild cognitive impairment ERP changes were found. TPM affected the cognitive functions in epilepsy patients reflected by the decreased full-scale intelligence quotient (FIQ). The imperative effects of TPM on visual perception function reflected by N170 were more obvious than that of VPA. Attention reflected by N270 was impaired after TPM treatment.

Antiepileptic Drugs and the Significance of Event-Related Potentials

The authors compared cognitive changes in epilepsy patients with or without antiepileptic drugs using event-related potential (ERP) N270 and P300. The patients were divided into three groups according to treatment type: carbamazepine, valproate acid (VPA), or no treatment. One control group composed of healthy subjects was included. The Mini-Mental State Examination detected no clinical dementia in all subjects. A modified Sternberg paradigm was used as a task when an ERP was recorded. When a stimulus was different from the memorized item (conflict condition), N270 was elicited in both controls and patients. All the three patient groups showed a delayed and smaller N270 than the control group. P300 was elicited when a stimulus was the same one as the memorized item (match condition), and its amplitude decreased in the VPA group. P300 latency did not differ among the four groups. ERP (N270 and P300) was abnormal in patients with epilepsy. These results indicate that antiepileptic drugs, especially VPA, might enhance the impairment of cognitive processing. N270 is more sensitive than P300 in the early detection of minor cognitive impairment in epileptics.