| |
Abstract:
An important question in cognitive neuroscience is how
different brain regions interact in mediating cognition. Recently,
TMS, in conjunction with positron emission tomography (PET), has
become a valuable tool in studying functional connectivity of brain
regions involved in specific tasks. During TMS, a magnetic field
applied to a region on the scalp induces intracranial excitatory
and inhibitory electrical currents that can alter regional neuronal
function, resulting in changes in performance, and also changes in
regional cerebral blood flow (rCBF) in other brain regions as
imaged by PET. Little is known about the exact neurobiological
mechanisms by which this alteration occurs. We investigated the
biological correlates of TMS and the relation between TMS and rCBF,
using a neurobiologically realistic large-scale model of the
ventral visual processing stream. Stimulation by simulated TMS led
to performance errors on a delayed-match-to-sample task, increasing
with TMS intensity. Generally, TMS increased rCBF in the stimulated
and connected regions; however, when TMS was applied only to the
inhibitory neuronal population there was decreased rCBF, suggesting
that stimulation of inhibitory neuronal populations results in rCBF
decreases, concurring with experimental findings of Paus and
colleagues. We also found that regions both directly and indirectly
connected to the stimulating site were affected by TMS. The
findings help elucidate the interpretation of TMS-induced rCBF
changes in disparate brain regions.
|
