Biological Sciences 300/301, Smith College | Neurophysiology

Case 6: Signaling by a face-selective neuron.

The figure below shows the responses of a single face-selective neuron from a monkey's temporal lobe to 36 different stimulus images. The stimulus image array includes four monkeys (b) and three people (c) with four different facial expressions each, and circles and squares in four colors (d). Under each stimulus image, a raster plot of the neuron's action potentials and a graph of the neuron's average firing rate are shown. Vertical calibration bars (100 spikes per second) appear in each firing rate graph at the time of stimulus presentation. The stimulus stays on for the duration of the dotted line under each graph. The lag between initial stimulus presentation and the start of the neuron's response is approximately 50 msec.

Discuss two questions with your neighbors and prepare to report to the class:

(1) Does this unit respond preferentially to a face's identity or emotional expression?
(2) Does the time course of the response have more than one phase?

Figure 1 Responses of a face-responsive neuron. a, Areas of brain examined. AP0 represents the position of the external auditory meatus; A14, A19, A22 and A24 represent anterior 14,19, 22 and 24mm, respectively. AMTS, anterior middle temporal sulcus; STS, superior temporal sulcus. b-d, Response diagrams of a single neuron for monkey, human and shape stimuli, respectively. Each diagram consists of a stimulus image, a raster plot of the response and a spike-density plot, in the first, second and third rows, respectively. The expressions of
four monkeys were neutral (A), pout-lips (B), full open-mouthed (C) and mid openmouthed (D). Those of 3 human models were neutral (A), happy (B), surprised (C) and angry (D). The colours of circles and rectangles were red (A), blue (B), green (C) and pink (D). For the spike-density plot, spikes per ms over all trials were summed and smoothed with a gaussian filter (s:d: 1/4 10 ms). The vertical line in each plot indicates the time of stimulus onset, and the dashed part in the abscissa indicates the duration of stimulus presentation.

Source: Sugase Y, Shigeru Y, Shoogo U & Kawano K (1999) Global and fine information coded by single neurons in the temporal visual cortex. Nature 400: 869-873.