Feed-forward modulation of the thalamocortical projections on different layers of the auditory cortex

Abstract

In the present study, feedforward modulation of the thalamocortical projections on the auditory cortex was investigated. The neuronal responses of the cortical neurons to electrical stimulation of the medial geniculate body and auditory stimulus were recorded with both intracellular and extracellular recordings. A stimulation electrode array was implanted in the MGB targeting the medial and ventral divisions. Electrode array for extracellular recording was implanted in the auditory cortex, recording neuronal responses from different layers simultaneously, while a sharp glass electrode was advanced to record neurons intracellularly. The stimulation sites in the MGB were confirmed with electrical lesion, while the recording neurons were labeled with biocytin after physiology. Neurons in the auditory cortex showed spontaneous activities with occasional oscillatory activity. A synchronized activity among from different layers could be found when there was an oscillation. The oscillation propagated from deep layers to the surface layers. The auditory responses appeared at layers III and IV before reaching to layers II and I, and layers V and VI. Stimulation of the MGv evoked mainly excitatory output in layers II to V, while stimulation of the MGm evoked mainly long-lasting inhibitory effect on the neurons in the deep layers. The present results would contribute to our understanding information processing mechanisms of feed-forward thalamocortical pathways and interaction among the layers in the cortex.