Relationship Between Spontaneous and Evoked Spike-Time Correlations in Primate Visual Cortex

Abstract

Coincident spikes have been implicated in vision-related processes such as feature binding, gain modulation, and long-distance communication. The source of these spike-time correlations is unknown. Although several studies have proposed that cortical spikes are correlated based on stimulus structure, others have suggested that spike-time correlations reflect ongoing cortical activity present even in the absence of a coherent visual stimulus. To examine this issue, we collected single-unit recordings from primary visual cortex (V1) of the anesthetized and paralyzed prosimian bush baby using a 100-electrode array. Spike-time correlations for pairs of cells were compared under three conditions: a moving grating at the cells' preferred orientation, an equiluminant blank screen, and a dark condition with eyes covered. The amplitudes, lags, and widths of cross-correlation histograms (CCHs) were strongly correlated between these conditions although for the blank stimulus and dark condition, the CCHs were broader with peaks lower in amplitude. In both preferred stimulus and blank conditions, the CCH amplitudes were greater when the cells within the pair had overlapping receptive fields and preferred similar orientations rather than nonoverlapping receptive fields and different orientations. These data suggest that spike-time correlations present in evoked activity are generated by mechanisms common to those operating in spontaneous conditions.

Effects of spatiotemporal stimulus properties on spike timing correlations in owl monkey primary somatosensory cortex

“…Several reports describe significant relationships between correlation magnitudes and average firing rates such that higher correlation magnitudes tend to occur when the two neurons in the pair have higher average firing rates (e.g., de la Rocha et al 2007;Greenberg et al 2008;Jermakowicz et al 2009), although others report very weak relationships (Samonds and Bonds 2005). Our data showed weak, positive relationships overall; however, this trend occurred primarily when nonadjacent digit locations were stimulated (Fig.…”

“…Geometric mean spike rate is commonly used to average firing rates of the two neurons in a correlated pair (e.g., Bair et al 2001;de la Rocha et al 2007;Greenberg et al 2008;Jermakowicz et al 2009). We took the average firing rate of each neuron during the epoch when the correlation was measured (0 to 700 ms).…”

“…Properties and possible roles of neuronal correlations have been studied in several brain areas, reviewed elsewhere (Jermakowicz and Casagrande 2007;Kohn et al 2009;Salinas and Sejnowski 2001). Correlated activities between pairs of neurons have been reported on extensively for the visual system (e.g., Bair et al 2001;Dong et al 2008;Fries et al 2001;Jermakowicz et al 2009;Kohn and Smith 2005), where stimulus properties and attention appear to influence changes in strength of correlations between neurons. Correlations in primate somatosensory cortex have been less extensively studied than those in visual cortex but may serve similar functions (e.g., Blake et al 2005;Hsiao et al 2002).…”

Packets of Sequential Neural Activity in Sensory Cortex

“…We found that population responses to different stimuli are subject to conserved spatiotemporal constraints, consistent with results in other modalities indicating conserved timing patterns in pairwise cross-correlograms [ 25 ]. One can imagine a number of ways in which the physical properties of a neural circuit could impose consistent constraints on the spike patterns it can generate.…”

“…8.2h ; R unanesth: spont-ton = 0.53 ± 0.17; p < 0.001). Similar consistent temporal patterns were also observed in the somatosensory cortex [ 9 ] and in the visual cortex [ 25 ] indicating that the sequential structure of spontaneous and evoked packets is a general feature of cortical processing.…”