Striatal recruitment during an implicit sequence learning task as measured by functional magnetic resonance imaging

Abstract

Prior research has repeatedly implicated the striatum in implicit sequence learning; however, imaging findings have been inconclusive with respect to the sub-territories and laterality involved. Using functional magnetic resonance imaging (fMRI), we studied brain activation profiles associated with performance of the serial reaction time task (SRT) in 10 normal right-handed males. Behavioral results indicate that significant implicit learning occurred, uncontaminated by significant explicit knowledge. Concatenated fMRI data from the entire cohort revealed significant right-lateralized activation in both the caudate and putamen. Analysis of fMRI data from individual subjects showed inter-individual variability as to the precise territories involved, including right as well as left caudate and putamen. Interestingly, all seven subjects who manifested robust learning effects exhibited significant activation within the putamen. Moreover, among those seven subjects, the magnitude of signal intensity change within the putamen correlated significantly with the magnitude of reaction time advantage achieved. These findings demonstrate right-sided striatal activation across subjects during implicit sequence learning, but also highlight interindividual variability with respect to the laterality and striatal subterritories involved. In particular, results from individual subjects suggest that, during the SRT, the reaction time advantage garnered via implicit sequence learning might be predominantly associated with activity within the putamen.

Distinct Contribution of the Striatum and Cerebellum to Motor Learning

“…In humans, pathological degenerative processes affecting the striatum [as in Parkinson's (PD) or Huntington's (HD) diseases], or circumscribed damage to the cerebellum, have been shown to produce an impairment on various skill-learning tasks, especially in the visuomotor modality (e.g., Doyon, Gaudreau, Laforce, Castonguay, Bédard, Bédard, & Bouchard, 1997a;Ferraro, Balota, & Connor, 1993;Harrington, York Haaland, Yeo, & Marder, 1990;Heindel, Salmon, Shults, Walicke, & Butters, 1989;Saint-Cyr, Taylor, & Lang, 1988;Sanes, Dimitrov, & Hallett, 1990). These findings have been corroborated by studies with healthy control subjects using modern brain-imaging techniques such as positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) in which hemodynamic changes have been observed in the striatum and/or the cerebellum during the incremental acquisition of visuomotor skills (e.g., Doyon, Owen, Petrides, Sziklas, & Evans, 1996b;Flament, Ellermann, Kim, Ugurbil, & Ebner, 1996;Grafton, Woods, & Mike, 1994;Jenkins, Brooks, Nixon, Frackowiak, & Passingham, 1994;Rauch et al, 1997).…”

Unconscious Activation of the Cognitive Control System in the Human Prefrontal Cortex

“…Some previous reports are in line with our results. Prefrontal activity has been reported in an implicit motor learning study, although the activity was only significant when a liberal threshold was used, and at that threshold, there was also activation in the visual cortex (Rauch et al, 1997). Moutoussis and Zeki (2002) have described a binocular masking paradigm (called binocular fusion) in which prefrontal activity was found to be higher when the volunteers did not see the presented figures.…”

The effect of explicit knowledge on sequence learning: A graded account

“…In these studies, however, implicit and explicit processes were exclusively associated with different training phases-a procedure that does not ensure that implicit and explicit components were effectively dissociated during the two training conditions. In a PET scan experiment, (Peigneux et al, 2000) reported the systematic activation of the striatum when participants were presented with a complex probabilistic sequence (see also Rauch et al, 1997). Sequence learning in experiments using this material is typically essentially implicit (e.g., Jiménez, Méndez & Cleeremans, 1996).…”