Cortical activity is under the control of ascending systems located in the brainstem and forebrain. Neurons of the parabrachial region (PBR) possess cholinergic/nitrergic terminals impinging on thalamic relay cells, which in turn send glutamatergic axons to the cortex. Basal forebrain (BF) cells send connections to the cortex, either cholinergic/nitrergic or GABAergic. Both systems control arousal levels and their stimulation can give rise to an activated EEG and a disruption of sleep or anaesthesia-induced oscillations. We have studied, on anaesthetized cats, the synchronization patterns among cortical neurons (n=60) under different levels of PBR and BF-induced activation. Ascending systems activation was regulated through electrical microstimulation applied to either PBR or BF. A multielectrode system was used for the extracellular recording of primary visual cortex (V1) neuronal groups. The electrocorticogram (ECoG) was also monitored.

Electrical stimulation evoked changes in neuronal oscillations and different synchronization patterns among V1 cells, depending upon the stimulation site. Frequency spectra, cross-correlation and time-dependent correlation strength were calculated for pairs of extracellular units. PBR stimulation induced a strong and long-lasting (up to 100 sec.) de-synchronization between pairs of cortical neurons, followed by a slow and continuous re-synchronization (lasting 75-200 sec.). BF stimulation evoked in most cases a relatively short de-synchronization (up to 10 sec.) followed by an abrupt re-synchronization. These results show key differences between the glutamatergic–mediated cortical activation induced by the PBR and the cholinergic/nitrergic activation induced by the BF, indicating the existence of different cortical functional routes for these ascending systems.

Supported by MEC-BFU2005-00502.