Distinct functional roles of narrow and broadband high-gamma activities in human primary somatosensory cortex

Abstract

Previous studies have shown that high-gamma (HG) activity in the primary visual cortex (V1) has distinct higher (broadband) and lower (narrowband) components with different functions and origins. However, it is unclear whether similar segregation exists in the primary somatosensory cortex (S1), and the origins and roles of HG activity in S1 remain unknown. Here, we investigate functional roles and origins of HG activity in S1 during tactile stimulation in humans and a rat model. In the human experiment, lower-frequency HG (50-70 Hz, LHG) was more sensitive to sustained tactile intensity compared with higher-frequency HG (70-150 Hz, HHG). HHG activity varied depending on the ratio of low and high mechanical frequencies, with its pattern reflecting a mixture of neural activities corresponding to them. Furthermore, classification analysis revealed that HHG activity contains more information about texture surfaces compared with LHG activity. In the rat experiment, we found that both HHG and LHG activities are strongest in the somatosensory input layer (layer IV), similar to findings in V1. Interestingly, spike-triggered local field potential (stLFP) analysis revealed significant HG oscillations exclusively in layer IV, indicating a dominant coupling between neuronal firing and HG oscillations in this layer. In summary, HHG activity is associated with detecting changes in the rate of contact force and subtle skin deformations whereas LHG activity reflects the absolute amount of applied contact force. Finally, both HHG and LHG originated in layer IV of S1. NEW & NOTEWORTHY We investigated the functional roles and origins of high-gamma (HG) activity in the primary somatosensory cortex (S1). The higher-frequency component of HG activity is associated with detecting changes in the rate of contact force and subtle skin deformations whereas the lower-frequency component reflects the absolute magnitude of the applied contact force. Both types of HG activity were found to originate in layer IV of S1.