Info

500 ms u

FIGURE 8.1-2 Diagram of how a JPST diagram is generated from the simultaneous spike recording of two neurons with a common, periodic, transient input.

500 ms u

FIGURE 8.1-2 Diagram of how a JPST diagram is generated from the simultaneous spike recording of two neurons with a common, periodic, transient input.

diagonal is represented by three parallel lines in the figure. In circuit F, both A and B are driven by the stimulus, and also A drives B. Thus, broad bands parallel to the t and u axes from S are seen; as well as diffuse density on the diagonal from the A ^ B connection. The responses in G are similar to those in D and E. The sharp diagonal band in the lower JPST diagram is the result of taking data from neurons B and C (presumably one would see that same JPST response from A and C, from symmetry). The diffuse diagonal band in the upper JPST figure is from a vs. B and the presence of three independent noise sources.

Finally, in the circuit of H, the stimulus excites both A and B. C, if not inhibited by S, drives B from an excitatory input from A. The JPST diagram shows a greater latency in the response of A than B, and the interrupted, sharp diagonal is the result of the stimulus inhibiting the C interneuron whereby A drives B.

FIGURE 8.1-3 (A to H) Simple neural configurations capable of producing the associated JPST diagrams. Light gray, sparse random points; dark gray, denser random dots; dark lines, dense lines of dots. Note in H that an inhibitory synapse to interneuron C causes a break in the diagonal line. See text for descriptions.

FIGURE 8.1-3 (Continued)

Other interesting neural circuit scenarios can be devised and described with the JPST technique. More challenging to interpret are the three-neuron, three-dimensional JPST dot volume displays described by Kristan and Gerstein (1970). (The axes of a three-dimensional JPST cube are shown in Figure 8.1-4.) These authors generated three-dimensional JPST volume dot displays in stereo pairs from three interneurons in the pleural ganglion of the sea-slug, Aplysia. The stereoscopic pairs permit viewing the dot density in a three-dimensional volume, rather than as a projection on a two-dimensional page. Interpretation of three-dimensional JPST

Neural circuit

JPST Diagram

Q -^Nc"

FIGURE 8.1-3 (Continued)

JPST Diagram

FIGURE 8.1-3 (Continued)

point volume displays takes some experience. Kristan and Gerstein (1970) offer some advice:

Bands of increased point density parallel to the three coordinate axes [t, u, v] represent the direct effects of the stimulus on the firing of the observed neurons. The lack of symmetry in the scatter diagram shows that the three neurons responded with different temporal patterns. Diagonal bands of increased point density, which are most visible near the ac and ab planes, correspond to the time structure of the probability for nearly simultaneous firing of the corresponding neuron pairs. Finally, a band of increased point density along the principal diagonal of the [display] cube represents the enhanced probability for nearly simultaneous firing of all three neurons.

FIGURE 8.1-4 A three-dimensional JPST cube display. Correlations in the firing of three neurons can be studied. See text for description.

The three-dimensional JPST cube shown schematically in Figure 8.1-4 would normally be filled with a random volume of dots because of independent random factors causing all three neurons to fire in the absence of stimulus. The bold line in the AC plane is because A drives C in a nearly 1:1 manner. The bands in the AB plane are because the stimulus drives neuron A in an uncertain manner. Finally, the dense line running along the cube diagonal from the origin is because the stimulus also drives neurons A, B, and C in a nearly 1:1:1 manner.

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