PMID-28739915 Interactions between feedback and lateral connections in the primary visual cortex
- Liang H1, Gong X1, Chen M2,3, Yan Y2,3, Li W4,3, Gilbert CD5.
- Extracellular ephys on V1 and V4 neurons in macaque monkeys trained on a fixation and saccade task.
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- Contour task: monkeys had to select the patch of lines, chosen to stimulate the recorded receptive fields, which had a continuous contour in it (again chosen to elicit a response in the recorded V1 / V4 neurons).
- Variable length of the contour: 1, 3, 5, 7 bars. First part of analysis: only 7-bar trials.
- Granger causality (GC) in V1 horizontal connectivity decreased significantly in the 0-30Hz band after taking into account V4 activity. Hence, V4 explains some of the causal activity in V1.
- This result holds both with contour-contour (e.g. cells both tuned to the contours in V1), contour-background, and background-background.
- Yet there was a greater change in the contour-BG and BG-contour cells when V4 was taken into account (Granger causality is directional, like KL divergence).
- This result passes the shuffle test, where tria identities were shuffled.
- True also when LFP is measured.
- That said .. even though GC is sensitive to temporal features, might be nice to control with a distant area.
- See supplementary figures (of which there are a lot) for the controls.
- Summarily: Feedback from V4 strengthens V1 lateral connections.
- Then they looked at trials with a variable number of contour bars.
- V4 seems to have a greater GC influence on background cells relative to contour cells.
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- Using conditional GC, lateral interactions in V1 contribute more to contour integration than V4.
- Greater GC in correct trials than incorrect trials.
- Note: differences in firing rate can affect estimation of GC. Hence, some advise using thinning of the spike trains to yield parity.
- Note: refs for horizontal connections in V1 [7-10, 37]
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