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 physiologic interactions between spatially and functionally distinct cortical somatosensory systems. The OIS response magnitude was evaluated after simultaneous stimulation of single whiskers and forelimb digits. Whisker C1 was deflected at a frequency of 10 Hz for 2 seconds while low- or high-intensity vibratory stimuli were applied to forelimb digits. The OIS responses to simultaneous whisker and forelimb stimulation were compared with lone whisker stimulated controls. Overall, addition of a second stimulus caused decreases in barrel cortex response magnitude. Three different response patterns were detected within individual trial sets. Modulation of barrel cortex evoked potentials provided evidence that changes in OIS responses observed here may be partially influenced by vascular responses to changes in neuronal activity. However, OIS responses in the barrel region during lone forelimb stimulation that were unaccompanied by evoked potentials suggested the possibility of independent vascular dynamic influences on response modulation. This study demonstrates that cortical responses at the level of primary sensory processing may be significantly influenced by activity in adjacent regions. Furthermore, it reveals that vascular and neuronal characteristics of interregional modulation do not co-localize and may produce responses in which one component increases while the other decreases.