Evidence for the emergence of relative navigational responding in male C57BL/6J mice in a land-based task

We recently reported that male C57BL/6J mice navigate in spatial tasks, such as the
Morris water maze MWM, by swimming in a particular direction to a location relative to poolbased
cues, rather than to an absolute location defined by room-based cues. Neural mechanisms
supporting this bias in rodents for relative responding rather than absolute responding in spatial
tasks are not yet understood. Anterior thalamic neurons discharge according to the current
directional heading of the animal. The contribution of head direction HD cell activity to
navigation has been difficult to elucidate. Selective inactivation of anterior thalamic nuclei ATN
by microinfusion of muscimol or fluorophore-conjugated muscimol caused a near complete shift
in preference from relative to absolute responding. Interestingly, inactivation of the dorsal CA1
region of the hippocampus did not affect relative responding. A land based version of the MWM
has been developed to permit the recording of anterior thalamic HD cells during spatial search
behavior. These experiments have been conducted to further examine the contribution of the HD
cell activity to relative responding during spatial navigation.