The Journal of Neuroscience, May 1, 1999, 19(9):3567-3579
Patterns of Synchronization in the Superior Colliculus of
Anesthetized Cats
Michael
Brecht,
Wolf
Singer, and
Andreas K.
Engel
Max-Planck-Institut für Hirnforschung, 60528 Frankfurt,
Germany
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 problems could be overcome by
synchronization of neuronal discharges, because it allows the selection
of a subset of distributed responses for further joint processing. To
assess the putative role of such a temporal binding mechanism in the
SC, we have applied correlation analysis to visually evoked collicular
activity. We performed recordings of single-unit and multiunit activity
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 
- and 
-frequency range. Significantly modulated
cross-correlograms were observed in 50% (128 of 258) of the collicular
multiunit recording pairs, and for these pairs significant correlations
occurred in 44% of the stimulation epochs. For the single-unit pairs,
significant interactions were observed in 14 of 48 cases studied
(29%). Collicular cross-correlograms were often oscillatory, and these
oscillations covered a broad frequency range of up to 100 Hz, with a
predominance of oscillation frequencies in the - and -range. In
the majority of the significant correlograms (64%) the phase lag of
the center peak was <5 msec. The probability of collicular
synchronization increased with the overlap of the receptive fields and
the proximity of the recording sites. Correlations were also observed
between cells in the superficial and deep SC layers. Collicular
synchronization required activation of the respective cells with a
single coherent stimulus and broke 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.
Key words:
synchronization; cell assembly; oscillation; cat; superior colliculus; correlation analysis
Copyright © 1999 Society for Neuroscience 0270-6474/99/1993567-13$05.00/0
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