Theta oscillations are a hallmark of hippocampal activity across mammals and play a critical role in many hippocampal models of memory and spatial navigation. To reconcile the cross-species differences observed in the presence and properties of theta, we recorded hippocampal local field potentials in rats and ferrets during auditory and visual localisation tasks designed to vary locomotion and sensory attention. Here, we show that theta oscillations occur during locomotion in both ferrets and rats, however during periods of immobility, theta oscillations persist in the ferret, contrasting starkly with the switch to large irregular activity (LIA) in the rat. Theta during immobility in the ferret is identified as analogous to Type 2 theta that has been observed in rodents due to its sensitivity to atropine, and is modulated by behavioural state with the strongest theta observed during reward epochs. These results demonstrate that even under similar behavioural conditions, differences exist between species in the relationship between theta and behavioural state.

Theta oscillations are a hallmark of hippocampal activity across mammalian species and play a critical role in many hippocampal models of memory and spatial navigation. To attempt to reconcile the cross-species differences observed in the presence and properties of theta, we recorded hippocampal local field potentials in rats and ferrets during a localisation task designed to vary locomotion and sensory attention. Here we show that theta oscillations occur during locomotion in both the ferret and rat, however during periods of immobility, theta oscillations persisted in the ferret, contrasting starkly with the switch to large irregular activity (LIA) in the rat. Theta during immobility in the ferret was identified as Type 2 theta due to its sensitivity to atropine and was modulated by behavioural state, with the strongest theta observed during reward epochs. These results demonstrate that even under similar behavioural conditions, there is a variable relationship between theta and behavioural state across different species.