Primary somatosensory contextual modulation is encoded by oscillation frequency change

• Very early somatosensory evoked responses show context-dependent modulation by auditory stimuli.
• Our delay differential equation model strongly suggests cortico-thalamic feedback in primary somatosensory processing.
• Frequency encoding, in contrast to network coupling, seems to play an important role in contextual modulation in the somatosensory thalamo-cortical network.

ObjectiveThis study characterized thalamo-cortical communication by assessing the effect of context-dependent modulation on the very early somatosensory evoked high-frequency oscillations (HF oscillations).MethodsWe applied electrical stimuli to the median nerve together with an auditory oddball paradigm, presenting standard and deviant target tones representing differential cognitive contexts to the constantly repeated electrical stimulation. Median nerve stimulation without auditory stimulation served as unimodal control.ResultsA model consisting of one subcortical (near thalamus) and two cortical (Brodmann areas 1 and 3b) dipolar sources explained the measured HF oscillations. Both at subcortical and the cortical levels HF oscillations were significantly smaller during bimodal (somatosensory plus auditory) than unimodal (somatosensory only) stimulation. A delay differential equation model was developed to investigate interactions within the 3-node thalamo-cortical network. Importantly, a significant change in the eigenfrequency of Brodmann area 3b was related to the context-dependent modulation, while there was no change in the network coupling.ConclusionThis model strongly suggests cortico-thalamic feedback from both cortical Brodmann areas 1 and 3b to the thalamus. With the 3-node network model, thalamo-cortical feedback could be described.SignificanceFrequency encoding plays an important role in contextual modulation in the somatosensory thalamo-cortical network.