434 demonstrated in patients with amnesia. Our Wndings sug- gest that some knowledge of the Wxed sequence did not inXuence implicit learning in either group of participants. Thus, limited explicit knowledge of the sequence cannot explain the diVerence in results on the PLT between the patient and the control groups. As already outlined in the Introduction and in our pre- vious study on implicit learning in patients with Parkin- son’s disease or Alzheimer’s disease (Van Tilborg and Hulstijn 2010), sequential motor skills are based on mul- tiple processes. Sequences can represent the order in which the stimuli occur, such as a visuospatial represen- tation, or the order in which the associated movements are made, e.g., the sequence of key presses. These two types of representation may also be dissociated at a neu- rocognitive level. Hikosaka et al. (1999) and Nakahara Doya and Hikosaka (2001) argue that a visual loop exists that is implicated in the representation of visual coordi- nates and that is distinct from a motor loop, which is implicated in the representation of motor coordinates. The spatial loop comprises the association cortex (espe- cially the prefrontal cortex) and the anterior portion of the basal ganglia, while the motor loop comprises the premotor–motor cortex (especially the SMA) and the middle portion of the basal ganglia (Hikosaka et al. 1999). It can be hypothesized that implicit learning involving the visual loop is compromised in patients with KorsakoV’s syndrome, because diencephalic regions are damaged and prefrontal regions are atrophic in these patients. This might explain why implicit learn- ing was intact when assessed with the time measures and compromised when assessed with the number of errors on the PLT. Since in the PLT the spatial aspects are more pronounced compared to the SRTT, these tasks show diVerent results. In conclusion, our Wndings conWrm the conjecture that implicit learning is compromised in patients with KorsakoV’s syndrome if the task has a strong spatial response component as in the PLT, but is spared if the task has a minimal spatial response component, as in the traditional SRTT. Thus, conclusions drawn about the extent of a patient’s implicit learning abilities need to take the type of task into account. Smith and McDowall (2006) have already argued that SRTT sequence learning is not a unitary phenomenon handled by a single gen- eral-purpose sequence learning system. We contend that the same might be true for the PLT, in which the expec- tation of the spatial location of the next target might be separated from learning to make the right movement toward the new target. Our Wndings emphasize the importance of discriminating between time and error measures in motor learning tasks. 123 Exp Brain Res (2011) 214:427–435 Open Access This article is distributed under the terms of the Crea- tive Commons Attribution Noncommercial License which permits any noncommercial use, distribution, and reproduction in any medium, provided the original author(s) and source are credited. References American Psychiatric Association (1994) Diagnostic and statistical manual of mental disorders, 4th edn. American Psychiatric Asso- ciation, Washington, DC Chun MM, Phelps EA (1999) Memory deWcits for implicit contextual information in amnesic subjects with hippocampal damage. Nat Neurosci 2:844–847 De Jong WP, Hulstijn W, Kosterman BJM, Smits-Engelsman BCM (1996) OASIS software and its application in experimental hand- writing research. In: Simner ML, Leedham CG, Thomassen AJWM (eds) Handwriting and drawing research: basic and ap- plied issues. IOS Press, Amsterdam, pp 429–440 Folstein MF, Folstein SE, McHugh PR (1975) Mini-Mental State: a practical method of grading the cognitive state of patients for the clinician. J Psychiat Res 12:189–198 Hikosaka O, Nakahara H, Rand MK, Sakai K, Lu X, Nakamura K, Miyachi S, Doya K (1999) Parallel neural networks for learning sequential procedures. Trends Neurosci 22:464–471 Knopman DS, Nissen MJ (1987) Implicit learning in patients with probable Alzheimer’s disease. Neurology 37:784–788 Kopelman MD (2002) Disorders of memory. Brain 125:2152–2190 Mayes RA (1988) Human organic memory disorders. Cambridge University Press, Cambridge Nakahara H, Doya K, Hikosaka O (2001) Parallel cortico-basal ganglia mechanisms for acquisition and execution of visuomotor sequences: a computational approach. J Cognitive Neurosci 13: 626–647 Nelson HE, O`Connell A (1978) Dementia: the estimation of premor- bid intelligence levels using the new adult reading test. Cortex 14:234–244 Nissen MJ, Bullemer P (1987) Attentional requirements of learning: evidence from performance measures. Cognitive Psychol 19:1– 32 Nissen MJ, Willingham D, Hartman M (1989) Explicit and implicit remembering: when is learning preserved in amnesia? Neuro- psychologia 27:341–352 Oslin D, Atkinson RM, Smith DM, Hendrie H (1998) Alcohol related dementia: proposed clinical criteria. Int J Geriatr Psych 13:203– 212 Postma A, Van Asselen M, Keuper O, Wester AJ, Kessels RPC (2006) Spatial and temporal order memory in KorsakoV patients. J Int Neuropsychol Soc 12:327–336 Postma A, Antonides R, Wester AJ, Kessels RPC (2008) Spared unconscious inXuences of spatial memory in diencephalic amne- sia. Exp Brain Res 190:125–133 Schacter DL (1987) Implicit memory: history and current status. J Exp Psychol Learn Mem Cogn 13:501–518 Schmidt A, Wrisberg CA (2000) Motor learning and performance, 2nd edn. Human Kinetics, Champaign Smith JG, McDowall J (2006) The implicit sequence learning deWcit in patients with Parkinson’s disease: a matter of impaired sequence integration? Neuropsychologia 44:275–288 Squire LR (1992) Declarative and nondeclarative memory: multiple brain systems supporting learning and memory. J Cogn Neurosci 4:232–243 Squire LR, Zola-Morgan S (1988) Memory: brain systems and behav- iour. Trends Neurosci 102:210–221