Patterns of synchronization in the superior colliculus of anesthetized cats

Sensorimotor transformations in the mammalian superior colliculus (SC) are mediated by large sets of distributed neurons. For such distributed coding systems, stimulus superposition poses problems attributable to the merging of neural populations coding for different stimuli. Such superposition prob lems could be overcome by synchronization of neuronal discharges, because i t allows the selection of a subset of distributed responses for further joi nt processing. To assess the putative role of such a temporal binding mecha nism in the SC, we have applied correlation analysis to visually evoked col licular activity. We performed recordings of single-unit and multiunit acti vity in the SC of anesthetized and paralyzed cats with multiple electrodes. Autocorrelation analysis revealed that collicular neurons often discharged in broad (20-100 msec) bursts or with an oscillatory patterning in the alp ha- and beta-frequency range. Significantly modulated cross-correlograms we re observed in 50% (128 of 258) of the collicular multiunit recording pairs , and for these pairs significant correlations occurred in 44% of the stimu lation epochs. For the single-unit pairs, significant interactions were obs erved in 14 of 48 cases studied (29%). Collicular cross-correlograms were o ften oscillatory, and these oscillations covered a broad frequency range of up to 100 Hz, with a predominance of oscillation frequencies in the alpha- and beta-range. In the majority of the significant correlograms (64%) the phase lag of the center peak was <5 msec. The probability of collicular syn chronization increased with the overlap of the receptive fields and the pro ximity of the recording sites. Correlations were also observed between cell s in the superficial and deep SC layers. Collicular synchronization require d activation of the respective cells with a single coherent stimulus and br oke down when the neurons were activated with two different stimuli. These data are consistent with the notion that collicular synchrony could define assemblies of functionally related cells.