OPTICAL INTRINSIC SIGNAL IMAGING RESPONSES ARE MODULATED IN RODENT SOMATOSENSORY CORTEX DURING SIMULTANEOUS WHISKER AND FORELIMB STIMULATION

Optical intrinsic signal imaging (OIS) was used to investigate physiol ogic interactions between spatially and functionally distinct cortical somatosensory systems. The OIS response magnitude was evaluated after simultaneous stimulation of single whiskers and forelimb digits. Whis ker Cl was deflected at a frequency of 10 Hz for 2 seconds while low- or high-intensity vibratory stimuli were applied to forelimb digits. T he OIS responses to simultaneous whisker acid forelimb stimulation wer e compared with lone whisker stimulated controls. Overall, addition of a second stimulus caused decreases in barrel cortex response magnitud e. Three different response patterns were detected within individual t rial sets. Modulation of barrel cortex evoked potentials provided evid ence that changes in OIS responses observed here may be partially infl uenced by vascular responses to changes in neuronal activity. However, OIS responses in the barrel region during lone forelimb stimulation t hat were unaccompanied by evoked potentials suggested the possibility of independent vascular dynamic influences on response modulation. Thi s study demonstrates that cortical responses at the level of primary s ensory processing may be significantly influenced by activity in adjac ent regions. Furthermore, it reveals that vascular and neuronal charac teristics of interregional modulation do not co-localize and may produ ce responses in which one component increases while the other decrease s.