Figure 1.

Theta frequency during isolated acceleration events correlates with positive acceleration, but not with negative acceleration or speed

(A) Left: scheme of the bottomless car running along a 4-m linear track and pulled by a motor. Right: detail showing the minimalistic design of the bottomless car.

(B) Instantaneous acceleration (left axes, mean: black dashed line, SD: gray area) and theta frequency (right axes, hippocampus: orange, MEC: red) averaged over 544 repetitions of an accelerating (top) or decelerating (bottom) speed step (rat 14,570). Instantaneous speed is shown underneath in shades of green (horizontal bars; transitions between 6 cm/s and 36 cm/s) and in insets at the top right.

(C) Examples of 1-s long EEG traces cut around the acceleration (light blue) or deceleration (dark blue) onsets, averaged over >20 similar repetitions and paired by similarity (high Pearson correlation) during the first half of the plot (one pair of average examples per row).

(D) Mean acceleration (top) and MEC theta frequency (bottom) for all possible speed steps obtained from pseudo-randomly alternating between four speeds in a four-speed protocol (7, 14, 21, and 28 cm s⁻¹; color code indicates acceleration group independently of speed). Dashed lines indicate 1^st and 99^th percentiles of the data during uniform motion. Black area: acceleration segment (60–260 ms after onset) used for quantification.

(E) MEC theta frequency (color coded) averaged across acceleration segments for the 16 curves in (D), arranged according to initial and final speed. Arrows indicate the direction of diagonals along which mean speed and acceleration increase.

(F) MEC (red) and hippocampal (orange) theta frequency as in (E) but pooling together all events belonging to the same acceleration group (mean ± SEM).

(G) Theta frequency during uniform motion at each of the four speeds for hippocampus (Hipp.) and MEC (mean ± SEM).