a) Traces: PSTHs across trials, sorted by duration into 5 groups.
Each PSTH is normalized to its maximum. Red dots: 30% of maximum.
Black lines: values of joystick press-aligned time
tpress (cell 1), joystick release-aligned
time trelease (cell 2) or sound frequency
f (cell 3) that best fit the red symbols. These fits
are for illustration purposes; the actual model maximized the
cross-correlation of PSTHs by aligning them to a linear combination of
tpress,
trelease, and f. Cells shown
are the same as in Extended Data Fig.
7. b) Fits of the model to all firing fields produced CA1
neurons. Axes are coefficients indicating the relative contribution of
tpress,
trelease, and f to the optimal
alignment of PSTHs. c) Contour plot of the density of points in (b),
illustrating 3 clusters. d) Distribution of fields belonging to each of the
3 clusters in (c) throughout the task. Time is linearly warped between the
press and the release of the joystick. Error bars: 95% multinomial
confidence intervals. Across all 411 fields from 341 recorded CA1 neurons
with a peak of a firing field occurring during the sound presentation
period, press-aligned, release-aligned, and frequency-aligned fields
accounted for 26%, 23% and 51% of the population,
respectively. (e–f) Same plots as in (b–d), but for 213
firing fields produced by 186 MEC neurons. In MEC, there was a larger
fraction of frequency-aligned fields (17%, 20% and
63% for the three types; p<0.01 χ2 test for
comparison to CA1). The three clusters in were not perfectly separated; in
fact, some firing fields had significantly non-zero regression coefficients
for more than one task parameter: 14% in CA1 and 21% in MEC
(p<0.01, bootstrap analysis).