Fig. 6

Superior colliculus (SC) activity during memory-guided microsaccades. a The top panel shows radial eye position aligned on microsaccade onset (for memory-guided microsaccades <1^o). All traces were aligned to start (on the vertical axis) from the same eye position. Most movements had a radial amplitude <30 min arc (0.5^o). These movements were selected relative to the response field (RF) as assessed from the analysis in b. The bottom panel shows microsaccade-aligned firing rate. Classic SC microsaccade-related activity¹⁸ was observed for memory-guided microsaccades. Each row of tick marks shows the neuron’s discharge for an individual movement from the top panel, and the rows are sorted by memory-guided microsaccade amplitude (black for <30 min arc; gray for 30–60 min arc). Even the smallest memory-guided microsaccades were associated with SC microsaccade-related discharge¹⁸. The gray bar on the x-axis indicates the analysis window used in b. Error bars denote 95% confidence intervals. b Movement RF of the same neuron. For each movement displacement, plotted in log-polar coordinates¹⁹, we plotted mean firing rate from the measurement interval in a. The neuron, from the right SC, exhibited a movement RF on the contralateral side along an oblique upward direction. The neuron clearly responded for memory-guided microsaccades as small as 0.1° (6 min arc). The origin of the log-polar plot denotes 0.03° radial amplitude. The inset shows spike waveforms from every 100^th spike recorded in the task (gray; 682 waveforms); red shows the average spike waveform (and 95% confidence intervals) across all recorded spikes