Head direction cell instability in the anterior dorsal nucleus of the thalamus following intraseptal microinfusions of the GABAA agonist muscimol
Head direction (HD) cells and theta oscillations are thought to be part of a network mediating navigational behavior. Intraseptal infusions of muscimol eliminates theta and produces navigational deficits. The present investigation sought to characterize the effects of septal inactivation using muscimol on (1) the basic directional characteristics of HD cells, (2) the control of the HD cell network by visual landmarks, and (3) the maintenance of a stable preferred direction (PD) using idiothetic cues in darkness. Blockade of theta by medial septal infusions of muscimol produced a population of HD cells with PDs that shifted unpredictably between sessions, suggesting that landmark control was affected. Further, a significant population of HD cells was unable to maintain stable PDs when the animals locomoted in the dark, suggesting that idiothetic cue processing was affected. These findings suggest that theta oscillations are necessary for the directional stability of HD cells in anterodorsal thalamus.