Figure 3.

Spike density histograms illustrating how the size of an expected reward can modulate spatial information held in working memory. The graphs illustrate neuronal activity as animals remember different locations on a computer screen under the expectancy of receiving either a small or a large reward for correct performance. The grey bar indicates the presentation of the mnemonic spatial cue. To enable clear visualization, the spatial data is collapsed into four groups consisting of 6 of the 24 possible spatial locations tested. The inset indicates the mean standardized firing rate of the neuron across the 24 spatial locations. a) When the subject expected a small reward, the neuron showed moderate spatial selectivity, which consisted of an increase in firing rate when the subject was remembering locations in the top right of the screen. When the subject expected a large reward for correct performance, spatial selectivity dramatically increased with a high firing rate for locations in the top right of the screen and a low firing rate for locations in the bottom left. b) A neuron that showed little spatial selectivity when the subject expected a small reward, but a dramatic increase in spatial selectivity when the subject expected a large reward.