State dependence of stimulus-induced variability tuning in macaque MT
Fig 3
Fano factors show significant tuning to motion direction in the alert state.
Fano factor across stimulus directions in example neurons from (A) alert and (B) anesthetized recordings in MT. Black dots indicate Fano factor by direction. Blue and orange traces show Fano factor values smoothed by a 30° moving window for the alert and anesthetized states, respectively. Red dashed lines indicate FF = 1, as expected for Poisson firing. (C) and (D) Population FF tuning curves in each behavioral state. (C) Gray traces show the Fano factors versus stimulus direction for all neurons in the alert experiments. Stimulus directions are aligned such that the preferred stimulus direction of each neuron is 0°. The median Fano factor across the population (green) is significantly tuned for the preferred direction. The gray dashed line indicates the median Fano factor in response to a stationary, or ‘null’, stimulus. Red dashed line is at FF = 1 as predicted for a Poisson process. (D) Same as (C) but for the anesthetized data. The median Fano factor is not tuned for stimulus direction. (E) Histogram distributions of Fano factor tuning indices (FFTI) from the alert (blue) and anesthetized (orange) experiments. Orange and blue traces are Gaussian best fit. The cartoon at top right shows how FFTI is calculated using the median trace from (C).