Thus, while pyramidal neurons were largely phase locked to the local theta waves, their spiking activity selleckchem was phase distributed when referenced to the theta cycle recorded from a single site. Assuming an 8 Hz theta signal (125 ms period) and a 10 mm flattened distance between the septal and temporal poles,

the half-theta cycle septotemporal phase shift of population unit firing between the two poles corresponds to 0.16 m/s velocity of activity travel, comparable to the speed of traveling activity observed in visual areas (Benucci et al., 2007). While theta coherence remained moderately high (c > 0.4; Figure 3E) along the entire long axis of the CA1 pyramidal layer, theta amplitude (or power) varied extensively (Figures 5A and 5B). Theta power between sites of the same hippocampal segment (Figure 5C; R > 0.81 REM; R > 0.75 RUN; p = 0.3, two-way ANOVA) and between the dorsal and intermediate segments (Figure 5D; R = 0.66 ± 0.132 REM; R = 0.64 ± 0.134 RUN) covaried reliably. In contrast, covariation of theta power between ventral sites versus intermediate and dorsal hippocampal locations was significantly MDV3100 price lower during both REM (Figure 5D; V-I: R = 0.39 ± 0.18; V-D: R = 0.32 ± 0.14; p < 0.001; two-way ANOVA) and RUN (Figure 5D; V-I:

R = 0.16 ± 0.14; V-D: R = 0.09 ± 0.082; p < 0.001; two-way ANOVA). A potential source of theta power modulation in different hippocampal segments is a “speed signal,” since the locomotion velocity of the animal is known to affect the amplitude of theta (McFarland et al., 1975). There was a significant correlation between running speed and theta power in the dorsal and intermediate from segments (Figures 5E and 5F;

Maurer et al., 2005; Montgomery et al., 2009) but not in the ventral segment (Figures 5E and 5F; p < 0.0001; ANOVA). Our results confirm and extend the prediction of Lubenov and Siapas (2009) that the phase of theta waves advances monotonically along the entire long axis of the hippocampus. In their “hippocampal circle” model, the septal and temporal poles are functionally “connected” by a full theta cycle. In contrast, we found ∼180° phase offset during exploration and a slower propagation of theta waves during REM, possibly due to the lower frequency of REM theta. A potential source of discrepancy between the two studies is the different axes of phase measurements. In the experiments of Lubenov and Siapas (2009), phase was computed from the combined anteroposterior and mediolateral propagation of theta waves in the dorsal hippocampus and extrapolated to correspond to 240°–360° along the septotemporal axis.

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