Thalamocortical structural connectivity abnormalities in drug-resistant generalized epilepsy: A diffusion tensor imaging study.

BACKGROUND AND PURPOSE: Epilepsy is one of the most common diseases of the nervous system. Approximately one-third of epilepsy cases are drug-resistant, among which generalized-onset seizures are very common. The present study aimed to analyze abnormalities of the thalamocortical fiber pathways in each hemisphere of the brains of patients with drug-resistant generalized epilepsy. MATERIALS AND METHODS: The thalamocortical structural pathways were identified by diffusion tensor imaging (DTI) in 15 patients with drug-resistant generalized epilepsy and 16 gender/age-matched controls. The thalami of both groups were parcellated into subregions according to the local thalamocortical connectivity pattern. DTI measures of thalamocortical connections were compared between the two groups. RESULTS: Probabilistic tractography analyses showed that fractional anisotropy of thalamocortical pathways in patients with epilepsy decreased significantly, and the radial diffusivity of the left thalamus pathways with homolateral motor and parietal-occipital cortical regions in the drug-resistant epilepsy group increased significantly. In addition to the right thalamus pathway and prefrontal cortical region, fractional anisotropy of all other pathways was inversely correlated with disease duration. CONCLUSION: The results provide evidence indicating widespread bilateral abnormalities in the thalamocortical pathways in epilepsy patients and imply that the degree of abnormality in the pathway increases with the disease duration.

Local field potentials are local events in the mouse auditory cortex.

Local field potentials (LFPs) and spikes (SPKs) sampled at the thalamocortical recipient layers represent the inputs from the thalamus and outputs to other layers. Previous studies have shown that SPK-constructed receptive fields (RFSPK) of cortical neurons are much smaller than LFP-constructed RFs (RFLFP). The difference in cortical RFLFP and RFSPK is therefore a plausible indication of local networking. The presence of a boarder RFLFP appears due to contamination, to some degree, from remote sites. Our studies of the mouse primary auditory cortex show that the best frequencies and minimum thresholds of RFSPK and RFLFP were similar. We also observed that the RFLFP area was only slightly larger than the RFSPK area, a very different finding from previous reports. The bandwidth of RFLFP was slightly broader than that of RFSPK at all levels. These data do not support the explanation that bioelectrical signals from distant sites impact on cortical LFP through volume conduction. That the cortical LFP represents a local event is further supported by comparisons of RFSPK and RFLFP after cortical inhibition by muscimol and cortical disinhibition by bicuculine. We conclude that the difference between RFSPK (output of cortical neurons) and RFLFP (input of cortical neurons) results from intracortical processing, including cortical lateral inhibition and excitation.