Hemodynamic observation and spike recording explain the neuronal deactivation origin of negative response in rat

Functional brain research has shown that the cerebral response to an external stimulus contains positive and negative signals. The positive signals are well studied, whereas explanations for the negative signals remain controversial. In this study, negative response was investigated using intrinsic optical imaging (OI) and a multi-electrode array (MEA) in rat with a hindlimb stimulus. The negative hemodynamic response (NHR) signals were measured by OI in contralateral and ipsilateral primary somatosensory forelimb, primary and secondary motor, and primary and secondary visual cortex areas. The spatial presentation of NHR signals showed diversity across subjects under an identical experimental paradigm. The NHR signals in different cortical areas had similar time courses but were in the opposite direction of the positive hemodynamic response (PHR) signals, and the amplitude of NHR signals was significantly smaller than that of PHR signals. Electrophysiological recording using an MEA in an NHR cortex area showed that spike activities decreased significantly during external stimulation, suggesting that the neuronal activity reduction has a strong relationship with the NHR signals. Our results highlight the importance of a negative response in a hemodynamics-based interpretation of neuroimaging signals.