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Abstract:
An EEG study with free-field auditory stimulation, and a
further study with monaural stimulation and combined multi-channel
EEG and MEG recording revealed the unsteadiness and abnormal
short-term habituation of arousal- (N1) and orienting response-
(P3a) related brain potentials after unilateral resection of
amygdala, hippocampus and a part of temporal lobe of the right
hemisphere. The distribution of mismatch negativity (MMN),
reflecting auditory sensory memory mechanisms, was distorted with
the main effect seen in frontal responses. Also the strength of the
temporal mismatch field in MEG was reduced in the resected
hemisphere. P3a waves were absent in responses to left ear
stimulation. These effects of resection in the right hemisphere
were seen especially when applying the stimuli to the left ear via
earphones. The results give further support to the previous
hypothesis on the role of hippocampus in orienting responses (P3a).
According to the present results, there also is a connection
between arousal mechanisms (N1) and amygdala-hippocampus complex.
The changes in frontal, electric MMN and the reduced strenght of
the magnetic temporal mismatch field may reflect distortion of
electric fields due to the resection and/or dysfunction of temporal
and frontal mismatch generators of this auditory sensory memory
mechanism.
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