Dynamic correlation of neuronal activity in rat cerebellar cortex modulated by behavior.

Sprague-Dawley rats (2-4 months old) were trained to perform a reaching-grasping task while their head was fixated and multielectrode recordings were performed in the ipsilateral cerebellar hemisphere. Multiunit (MU) activity was recorded with 2-3 electrodes in the Purkinje cell layer at various depths (1.5-4.5 mm) from the pial surface while the animal either performed the reaching-grasping task or was at rest. Recording sites were visually aligned along the transverse or the sagittal axis of Crus IIa. Excess correlations of MU spike activity were calculated at 10-ms time resolution using the joint peristimulus time histogram (JPSTH), to reveal the dynamics of cross-correlations corrected for nonstationarities in spike rates. Peak correlation amplitudes and areas were calculated separately for a time period preceding the movement and for a succeeding period during which the movement occurred. Correlations were compared across different paradigms: transversal versus sagittal alignment of recordings sites and behavior versus rest. No significant differences were found between transversally and sagittally aligned recording sites. Significant differences in peak correlation amplitude and/or peak area, however, were found both between premovement and movement time, as well as between both these time periods and periods while the animal was at rest.