| |
Abstract:
Abstract: Results from a target detection task in which a
proportion of the non-target stimuli were immediately repeated
showed that, relative to initial presentations, repeated
presentations elicited a less negative ERP waveform at frontal
electrode sites between 250-350ms and a less positive ERP waveform
at parietal sites between 300-600ms. Determining the neural tissue
responsible for these effects, however, is not a trivial matter.
One option is to take advantage of the spatial and temporal
sensitivity of magnetoencephalogram (MEG) recordings to localize
neural sources. Using brain surface current density mapping, we
found that repeated non-target stimuli elicited less brain activity
relative to first presentations at recording sites over
anterior-temporal and parietal cortex. This suggests that the
frontal effect in the ERP study was a consequence of reduced neural
activity in the temporal lobe whereas the parietal ERP effect was
due to a widespread reduction of parietal cortex activity. The
spatial and temporal distribution of the temporal lobe activity
reduction resembles results from single unit recordings in macaques
showing inferotemporal (IT) neurons that suppress their firing rate
when non-task relevant stimulus repetitions occur. The parietal
cortex reduction is similar to reductions in posterior cortical
activity obtained in neuroimaging studies of implicit
memory.
|
