The neural correlate of anticipatory pursuit movements in the Supplementary Eye Fields.
Anticipatory movements are actions starting before the occurrence of likely sensory events. In an experimental setting, this can be studied by having subjects pursue a moving dot of light appearing on a visual display. If the visual stimulus moves consistently in the same direction during a few presentations, subjects anticipate that it will likely continue to do so during the next presentation and the eyes will start to move in advance of the beginning of the next stimulus appearance. Anticipatory pursuit is a smooth movement of the eye occurring before the appearance of an expected moving target. The expectation of the subject is based on a subjective estimation of the probability that the target will move in a given direction. Although human subjects can be informed of the objective probability that a target will move in a given direction, they tend to rely heavily on past experience to guide their decision to move. Anticipatory pursuit has been extensively studied at the behavioral level. However, the neural mechanisms allowing this important behavior are unknown. Recently, it has been suggested that the SEF could play a role in using past experience to guide anticipatory pursuit. This hypothesis is currently being tested at the single neuron level. Indeed, it has been shown that neurons in the SEF are active during smooth pursuit in the absence of saccades (Heinen 1995), especially when predictable changes in target motion occur (Heinen and Liu 1997). In the behaving monkey, it has been shown that electrical microstimulation in the SEF can facilitate smooth pursuit initiation towards a moving target, suggesting that activation of the SEF might change the internal gain of the smooth pursuit pathway (Missal and Heinen 2001). Expectation of future target events could be altering the internal gain of smooth pursuit. We are currently investigating this hypothesis.