Parietal cortex subserves various cognitive
tasks, ranging from attention to visuo-motor skills. It is part
of a parieto-frontal network involved in attention, and part
of the visual dorsal stream, opposed to the visual ventral
stream, although increasing evidence suggests interchange
of information between them. In this study, co-registration
of Transcranial Magnetic Stimulation (TMS) and Electroencephalographic
activity (EEG) has been used to investigate
the spreading of cortical connections from the
parietal cortex in healthy volunteers. TMS on the left
parietal cortex activated a network of prefrontal regions in
the contra-lateral hemisphere in a time range of 102–
167 ms after the stimulus. Moreover, activation in the ipsilateral
middle temporal and fusiform gyri was observed at
171–177 ms after delivery of TMS. Findings suggest the
existence of late driven connections between parietal and
prefrontal regions that could partially represent the neural
pathway related to attention, even if, in this experiment, no
attentional processing was requested. Late connections
between dorsal and ventral streams were also evident,
confirming previous evidence about interchange of information
between them. Conclusively, the present investigation
confirms that a great amount of information spreads
from parietal cortex to different regions in the brain, supporting
the idea that connections are more complex and
articulated than those proposed. Present findings also
suggest that the simultaneous recording of EEG during the
application of TMS is a promising tool for the study of
connections in the brain.
