Figure 2: Network responses form discrete clusters as observed in vivo.

(a) Total number of spikes in response to 1,000 stimulus exposures (350 ms duration each), for each cell and each stimulus. (b) Same data as in a, with columns (network responses) sorted by similarity. The population responses fall within a limited number of discrete patterns. (c): Correlation matrix of columns of b. Each location i,j in this matrix represents the correlation between response vectors i and j in b. Clusters of highly correlated response patterns are readily apparent. (d) Correlation matrix of recorded responses in mouse auditory cortex for comparison, redrawn from data provided by Bathellier et al.⁵ using the same procedure as c. (e) Voltage traces of three neurons, two of which (2 and 39) belong to a common cluster and have similar selectivities and receptive fields, while the third (8) has a different selectivity and belongs to a different cluster. The voltage trace covers two stimulus presentation, followed by 100 ms stimulus-absent ‘relaxation’ periods indicated by dotted vertical lines (see Methods); the first stimulus is preferred by neurons 2 and 39, while the third is preferred by neuron 8. Neurons 2 and 39 show highly similar, though not identical traces, while cell 8 follows a very different activity pattern.