Inside Prefrontal Cortex
Layer III of dorsolateral prefrontal cortex: 500 pyramidal cells encode a spatial cue, then hold it for four seconds after the cue is withdrawn.
The idea
The camera sits in a volume the page labels Layer III pyramidal population, under the title Dorsolateral Prefrontal Cortex. Five hundred cells each prefer a direction. A cue turns that direction on, then the external drive stops, and the population is left to keep it.
The approach
The 500 cells fill a box 120 by 80 by 120 in the scene's units. Preferred directions fall into eight columns, 45 degrees apart, with a little scatter inside each column. A cell's colour is that preferred direction. When it is active the soma shifts from deep blue towards purple-white. Two thousand dim particles fill the gaps.
Top right, Task Phase uses four names: Ready, Encoding, Maintenance and Reset. Encoding lasts 800 ms and is drawn in amber. Maintenance lasts 4 seconds and is drawn in purple, with the remaining time in seconds. Reset lasts 2 seconds, then the next trial starts. The circle on the right holds a dot at the cue angle: amber and bright during Encoding, dim purple during Maintenance.
POPULATION ACTIVITY is a bar from blue to purple, filled from the mean activity of the 500 cells. Under it, the spike strip draws one tick per recent spike. The row is the neuron's index. The hue is that cell's preferred direction. The drawing places a tick by its age across a 3-second window, newer ticks to the right, though the simulation only keeps spikes from the last 500 ms, so they sit in the right-hand part of the strip. A dashed vertical line crosses it at four-fifths of the width. The corner counts neurons, cells above activity 0.3, and a firing rate in hertz.
Start Task runs the loop and relabels itself Stop. Toggle Flight starts on and drifts the camera through the volume. With flight off, dragging shifts the view and the wheel moves in and out. Speed cycles through 1×, 2× and 0.5×.
- 500 cells, preferred directions in eight columns 45 degrees apart
- Encoding is 800 ms and amber; Maintenance is 4 s and purple; Reset is 2 s
- The cue dot is amber during Encoding and dim purple during Maintenance
- Raster ticks take their hue from preferred direction; a dashed line sits at four-fifths of the strip
Play the current build: /simulations/inside-prefrontal-cortex .