RESEARCH NOTE Control of oculomotor reﬂexes: independent effects of strategic and automatic preparation Martijn Gerbrand Van Koningsbruggen Æ Robert D. Rafal Received: 20 February 2008 / Accepted: 9 November 2008 / Published online: 28 November 2008 Ó Springer-Verlag 2008 Abstract The reduction in saccade latency when the ﬁxation point is removed (ﬁxation offset effect–FOE) reﬂects the degree to which ﬁxation neurons are under inﬂuence by a stimulus at ﬁxation. Strategic manipulations of oculomotor readiness that bring these neurons under endogenous control reduce the magnitude of the FOE. Using an aging foreperiod paradigm, and the FOE as a marker for cortical control of reﬂexive ﬁxation, we showed that, for both prosaccades and antisaccades, increasing preparation across the foreperiod reduced both saccade latency and the FOE. Consistent with Los’s trace condi- tioning account, these effects reﬂected greater preparation for trials when the current short foreperiod was preceded by a trial with a short foreperiod. The FOE was also smaller for antisaccades than for prosaccades demonstrat- ing strategic modulation. However, the effects of trace conditioning were comparable in the two tasks, demon- strating that strategic and unconscious priming effects both independently modulate the control of ocular ﬁxation. Keywords Eye movements Á Preparatory activity Á Voluntary control Á Fixation offset effect Á Superior colliculus Á Anti saccades Á Visual grasp reﬂex Á Fixation reﬂex Introduction Easton argued that the neural circuits that subserve reﬂexes are the building blocks for more complex behavior; and that the nervous system routinely goes about its business through an orchestration of those circuits by cortical pro- cesses that activate or inhibit them (Easton 1972). The evolution of more complex behaviour required cortico- subcoritcal integration to regulate reﬂexes in the service of goal directed action (Ingle 1973; Rozin 1976). Eye movements provide an attractive model to study how pre- paratory states inﬂuence reﬂexive behavior. The current investigation employs the ﬁxation offset effect (FOE) as a marker task for probing the effects of strategic control and more automatic, non-speciﬁc preparation on oculomotor reﬂexes. The ﬁxation offset effect In the rostral pole of each superior colliculus (SC) are cells that are active during ﬁxation, even in the dark, and whose activity is further increased by a visual signal at ﬁxation (Munoz and Wurtz 1992, 1993b). These ﬁxation neurons help anchor the eyes at ﬁxation. Caudal to the ﬁxation neurons, and inhibited (either directly or indirectly) by them, are neurons (movement cells) whose activity moves the eyes to a new position (Munoz and Istvan 1998). Eye movements toward a peripheral target, then, are controlled by an opponent process: there is mutual inhibition between the visual grasp reﬂex (VGR), activated by abrupt signals in the visual periphery and mediated by movement neu- rons, and the ﬁxation reﬂex, activated by visual signals at ﬁxation and mediated by ﬁxation neurons. Together, the activity of these two types of cells determines when and where the eyes will move (Findlay and Walker 1999; Munoz and Fecteau 2002). The offset of a ﬁxated stimulus prior to, or simultaneous with, the onset of a peripheral target disinhibits the VGR M. G. Van Koningsbruggen (&) Á R. D. Rafal Wolfson Center for Clinical and Cognitive Neuroscience, School of Psychology, Bangor University, Bangor, UK e-mail: pss801@bangor.ac.uk 123 Exp Brain Res (2009) 192:761–768 DOI 10.1007/s00221-008-1655-7