Eye-neck coupling during optokinetic responses in head-fixed pigeons (Columba livia): influence of the flying behaviour

The effects of the behavioural context on the properties of slow and fast phases of the horizontal optokinetic nystagmus (OKN) and on the electromyographic neck response (EMG) were investigated in head-fixed pigeons. Responses in two situations were compared: (i) animals were hung in a harness ('resting' condition); (ii) animals in harness were subjected to a frontal airflow that provoked a flight posture ('flying' condition). During optokinetic stimuli the neck muscles responded in synchrony and in synergy with the eye nystagmus in both the 'resting' and the 'flying' conditions. In the 'resting' condition the neck activity was essentially correlated to the slow phase velocity of the eyes (eye SPV) whereas in the 'flying' condition, the neck response was also correlated to the eye position. The neck response was independent of the retinal slip velocity during the OKN. The velocity of the slow and fast phases of the OKN was not modified by flight. However, the 'flying' condition provoked an increase of the neck response by augmenting both its velocity gain (neck EMG/eye SPV) and its position gain (neck EMG/eye position). These results show that although an optokinetic stimulation results in synchronised eye and head motor commands in head-fixed pigeons, only the head motor command is modified by the behavioural context ('flying' vs. 'resting'). This strategy could help pigeons in reorienting their gaze during the flight.