Fig. 3: V1–V2 interaction transitions from feedforward-dominated shortly after stimulus onset to feedback-dominated during the spontaneous period.
a Inter-areal zero-delay population correlation increased throughout the trial, and was higher for spontaneous activity than for evoked activity. Zero-delay refers to spike counts taken in the same time window in the two areas (t1 = t2 in Fig. 2b). Black line shows the average across all recording sessions for which the V1 and V2 populations have aligned receptive fields. Shading indicates S.E.M. Dotted line shows average across all recording sessions where the V1 and V2 receptive fields are misaligned. Gray line shows average population correlation after shuffling trial correspondence between the two areas. b Population correlation functions for an example session (red: early evoked, yellow: late evoked; purple: spontaneous). Faded lines show population correlation functions after shuffling trial correspondence between the two areas (note that there are multiple superimposed lines). c Population correlations at all times during the trial. The horizontal axis represents the time delay between areas (t1 − t2), and the vertical axis represents time relative to stimulus onset (t1). Horizontal lines (red, yellow, and purple) indicate epochs used in b. Dashed vertical line indicates zero-delay population correlations shown in a. White area denotes times for which population correlations could not be computed: the V2 activity window had reached either the beginning or the end of the trial. Same session as in b. d Feedforward ratio for different epochs of evoked and spontaneous activity. Left panel shows sessions for which the V1 and V2 populations have aligned receptive fields; right panel shows sessions where the V1 and V2 receptive fields are misaligned. Feedforward ratio is defined as the difference between the area under the feedforward (positive delay) and feedback (negative delay) sides of the population correlation function, divided by their sum. Solid symbols show the average across all recording sessions, whereas open symbols correspond to each recording session. Insets show average feedforward ratios after shuffling trial correspondence between the two areas for each recording session (horizontal lines show 1 S.D. intervals, most of which are not visible because they are smaller than the width of the plotted symbol). e An early feedforward peak is only present in recording sessions where the V1 and V2 populations have aligned receptive fields. Peak height is measured after performing a jitter-correction to isolate fast timescale interactions (see Methods and Supplementary Fig. 3). Circles correspond to recording sessions for which the V1 and V2 populations have aligned receptive fields. Triangles correspond to sessions in which the V1 and V2 receptive fields are misaligned.
