Coding of peripheral electrical stimulation frequency in thalamocortical pathways.

Frequency information of the environment is an important feature for sensory perception. It has been demonstrated that cortical and thalamic neurons exhibited frequency-specific responses to peripheral stimulation. In the present study, we investigated the effects of 1-100 Hz peripheral electrical stimulations on various thalamic and cortical areas in awake rats. We used chronically implanted microelectrode arrays to record neural activities from the anterior cingulate cortex, primary somatosensory cortex, and medial dorsal and ventral posterior thalamus. The results revealed that cortical and thalamic neurons exhibited frequency-specific responses at both single-neuron and ensemble levels. Clusters of neurons responded to different frequency ranges with changes of both the peak firing rates and the phases of the peak responses in a stimulation cycle. Partial directed coherence analysis showed that information flowing between these recorded areas is also enhanced or inhibited in some frequency-specific pattern during stimulation. These evidences suggest that central nervous system may code environmental frequency information mainly with the activation of selected neural circuits according to their own intrinsic electrical properties. These properties, in turn, may facilitate or inhibit their responses when stimulation with specific frequency information arrives.