Rat hippocampal theta rhythm during sensory mismatch

Abstract

It has been suggested that sensory mismatch induces motion sickness, but its neural mechanisms remain unclear. To investigate this issue, theta waves in the hippocampal formation (HF) were studied during sensory mismatch by backward translocation in awake rats. A monopolar electrode was implanted into the dentate gyrus in the HF, from which local field potentials were recorded. The rats were placed on a treadmill affixed to a motion stage translocated along a figure 8-shaped track. The rats were trained to run forward on the treadmill at the same speed as that of forward translocation of the motion stage (a forward condition) before the experimental (recording) sessions. In the experimental sessions, the rats were initially tested in the forward condition, and then tested in a backward (mismatch) condition, in which the motion stage was turned around by 180 degrees before translocation. That is, the rats were moved backward by translocation of the stage although the rats ran forward on the treadmill. The theta (6-9 Hz) power was significantly increased in the backward condition compared with the forward condition. However, the theta power gradually decreased by repeated testing in the backward condition. Furthermore, backward translocation of the stage without locomotion did not increase theta power. These results suggest that the HF might function as a comparator to detect sensory mismatch, and that alteration in HF theta activity might induce motion sickness.

Rat thalamic neurons encode complex combinations of heading and movement directions and the trajectory route during translocation with sensory conflict

“…The present study provides additional evidence with respect to a role of the HD system in directional processing; the rodent HD system extracts different types of directional information (Figure 9) in different reference frames in a conflicting situation. The previous studies suggest the rats could adapt to backward translocation (Zou et al, 2009a; Aitake et al, 2011), and hippocampal neurons showed plastic changes in place fields after repeated experience of backward translocation in the same setup as in the present study (Zou et al, 2009b). The HD neurons reported in the present study might play important roles for spatial updating during the backward translocation.…”

“…However, it might be unlikely; first, the previous studies reported that although the backward movement increased hippocampal theta and sympathetic nervous activity, which corresponds to symptoms in motion sickness, the activity returned to the baseline level after repeated experience of this situation (Zou et al, 2009a; Aitake et al, 2011). This suggests that the rats could adapt to this situation.…”

“…In this backward translocation condition, idiothetic sensory inputs [visual (optic flow), vestibular inputs, and proprioceptive inputs or motor efferent copy] were mismatched; the proprioceptive inputs and/or motor efferent copy during locomotion (locomotion-related inputs) did not match the visual (optic flow)/vestibular inputs. Notably, although the rats showed increases in hippocampal theta power and sympathetic nervous activity, which is similar to symptoms in motion sickness (Zou et al, 2009a; Aitake et al, 2011), these changes returned to the baseline level after repeated exposure to the conflicting situation (Zou et al, 2009a; Aitake et al, 2011). These results suggest that the animals could adapt to this conflicting situation after repeated training, and that the rats could normally recognize the space in this condition.…”

“…The same apparatus as that in our previous papers (Dayawansa et al, 2006; Zou et al, 2009a,b; Aitake et al, 2011) was used. A stereotaxic apparatus with a transparent plastic enclosure for the semichronic recording (Nishijo and Norgren, 1990) and a treadmill were attached to the mobile stage (Figure 1A).…”

From ear to uncertainty: vestibular contributions to cognitive function

“…Many studies in alert animals have reported that theta rhythm in the frequency range of 6–9 Hz can be recorded during movement (see Zou et al, 2009 for a review). In fact, theta frequency has been shown to increase with increasing speed of locomotion (Jeewajee et al, 2008; Lever et al, 2009).…”