Brain : a journal of neurology
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Between attacks, migraine patients are characterized by potentiation instead of habituation of stimulation-evoked cortical responses. It is debated whether this is due to increased or decreased cortical excitability. We have studied the changes in visual cortex excitability by recording pattern-reversal visual evoked potentials (PR-VEP) after low- and high-frequency repetitive transcranial magnetic stimulation (rTMS), known respectively for their inhibitory and excitatory effect on the cortex. ⋯ There were no significant changes of PR-VEP amplitudes after 1 Hz rTMS in migraineurs and after 10 Hz rTMS in healthy volunteers, nor after sham stimulation. The recovery of a normal PR-VEP habituation pattern after high-frequency rTMS is probably due to activation of the visual cortex and the dishabituation in healthy volunteers to cortical inhibition. We conclude, therefore, that the deficient interictal PR-VEP habituation in migraine is due to a reduced, and not to an increased, pre-activation excitability level of the visual cortex.
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A key aspect of social cognition is the ability to infer other people's mental states, thoughts and feelings; referred to as 'theory of mind' (ToM). We tested the hypothesis that the changes in personality and behaviour seen in frontal variant frontotemporal dementia (fvFTD) may reflect impairment in this cognitive domain. Tests of ToM, executive and general neuropsychological ability were given to 19 fvFTD patients, a comparison group of Alzheimer's disease patients (n = 12) and matched healthy controls (n = 16). ⋯ Rank order of the fvFTD patients according to the magnitude of impairment on tests of ToM and their degree of frontal atrophy showed a striking concordance between ToM performances and ventromedial frontal damage. There was a significant correlation between the NPI score and more sophisticated tests of ToM in the fvFTD group. This study supports the hypothesis that patients with fvFTD, but not those with Alzheimer's disease, are impaired on tests of ToM, and may explain some of the abnormalities in interpersonal behaviour that characterize fvFTD.