Gaze pursuit, 'Attention pursuit' and their Effects on Cortical Activations

Introduction: An interesting or relevant moving object like an approaching car draws our attention on it and we follow the object by generating smooth pursuit eye movements (SPEM). Gaze and attention directions are usually conjunct and remain conjunct during SPEM. In this study we investigate whether gaze and attention directions can be split during pursuit. We intended to gain information about the cortical control of ocular tracking vs. attentive tracking and their interactions. Methods: We presented a horizontally and sinusoidally moving target for pursuit and simultaneously a stationary target for fixation. Gaze could be located on the pursuit target and attention on the fixation target or vice versa, or gaze and attention were located on the same target, either the pursuit or the fixation one. 12 healthy subjects were measured. Eye movements were recorded with the Freiburg MR-Eyetracker, cortical activations were measured via functional Magnetic Resonance Imaging (fMRI) (1.5T Siemens Avanto scanner). Results: Visual attention could be split from gaze during smooth pursuit eye movements without significant changes of pursuit performance. We found that gaze and attention pursuit similarly activated the cortical oculomotor network. Dissociation of gaze and attention directions led to increased activations. Attention specific activations were found solely in the posterior parietal cortex (PPC), independent of eye movements. A cue indicating a forthcoming attention task activated the cortical SPEM network during the rest period. Conclusion: We conclude that 'attention pursuit' occurs within the cortical SPEM network, supporting the premotor theory of Rizzolatti et al. 1987. The dissociation of attention from gaze (the shift of attention) seems to be processed specifically by PPC. The modulation of baseline attentive set (by a cue) might be due to changing the coherence level and thereby the sensitivity of a neuronal population.