Ann Graybiel (MIT)
A. David Redish (U. of Minnesota)
虫明 元 （東北大学）
"A New Look at Habit Learning"
The same brain that can construct language, music and mathematics also lets us develop habits of thought and action. These semi-automatic routines free us to think and attend to the world. But the habit system can also be hijacked by disease and drug exposure. This lecture will focus on the habit system of the brain and our remarkable ability to switch from conscious activity to nearly non-conscious behavior. The lecture will highlight research directed towards understanding how we make and break habits and how the neurobiology of the habit system is helping to advance understanding of human problems ranging from Parkinson's disease to obsessive-compulsive spectrum disorders and addiction. Clinical and experimental evidence suggests that our ability to acquire habits depends on the basal ganglia, deep forebrain structures that are interconnected with the frontal cortex in a series of loop circuits. The development of recording techniques for monitoring neural activity in awake behaving animals now makes it feasible to investigate what forms of neuronal representation are built up in the basal ganglia and cortico-basal ganglia loops as habits are acquired. Recordings from the striatum, the largest input side of the basal ganglia, suggest remarkable plasticity in the response properties of striatal neurons as animals learn sequential procedures and also as they undergo bouts of learning, extinction and reacquisition training. Single unit activity changes systematically through these bouts and so does ensemble activity. These results suggest that there is a form of 'neural exploration' followed by 'neural exploitation' in the basal ganglia as procedures are learned. After learning, the ensemble activity tends to emphasize the beginning and end of such procedures, as though setting up boundary states in higher-order representations. These and other findings support the view that basal ganglia-based circuits can build representations of sequential actions that facilitate their release or inhibition. Evidence suggests that the laying down of such representations involves genes expressed in basal ganglia-related networks, and there are promising molecular approaches to understanding learning mechanisms of the basal ganglia. Disorders of such basal ganglia plasticity could contribute to behavioral fixity and difficulty of initiation of behavior, as in Parkinson's disease, or to the excessive release of behaviors, as in Huntington's disease, or to the repetitive behaviors and thoughts characteristic of many neuropsychiatric disorders. The basal ganglia thus may influence not only motor pattern generators, but also cognitive pattern generators.
Fujii, N. and Graybiel, A.M. (2003) Representation of action sequence boundaries by macaque prefrontal cortical neurons. Science, 301:1246-1249.
Fujii, N. and Graybiel, A.M. (2005) Time-varying covariance of neural activities recorded in striatum and frontal cortex as monkeys perform sequential-saccade tasks. PNAS 102:9032-9037.
Barnes, T. Kubota, Y., Hu, D., Jin, D.Z., and Graybiel, A.M. (2005) Activity of striatal neurons reflects dynamic encoding and recoding of procedural memories. Nature 437:1158-1161.
DeCoteau WE, Thorn CA, Gibson DJ, Courtemanche R, Mitra P, Kubota Y, Graybiel AM (2007) Learning-related coordination of striatal and hippocampal theta rhythms during acquisition of a procedural maze task. PNAS 104:5644-5649.
A. David Redish
Neural coding in the hippocampus and striatum during decision-making
I will present our recent ensemble recordings and analyses from dorsal striatal and hippocampal recordings from rats running a repeating (looped), spatial decision task. In particular, we will present
analyses of within-day learning on these tasks. Hippocampal ensembles
show correlates related to fast, cognitive, early learning, while
dorsal striatal ensembles show correlates related to slower, more
habitual, later learning. These will be placed in the context of a
role of striatum and hippocampus in decision-making.
Neural mechanisms underlying goal-directed action planning
To achieve a behavioral goal in a complex environment, we must plan multiple steps of action. On planning a series of actions, we anticipate future events that will occur as a result of each action and mentally organize the temporal sequence of events. To investigate the involvement of the lateral prefrontal cortex (PFC) in such multi-step planning, we examined neuronal activity in the PFC while monkeys performed an action-planning task that required the planning of stepwise multiple actions to reach a goal.
This paper will cover neuronal representation of series of actions, goal sub-goal transformation, and synchrony of prefrontal neurons. In our previous studies, we found PFC neurons reflected final goals, immediate goals during the preparatory period. We also found some PFC neurons reflected each of /all/ forthcoming step of actions during the preparatory period and increased their activity step by step during the execution period. Our data suggest that the PFC is involved primarily in planning multiple future events that occur as a consequence of behavioral actions.
Mushiake H, Saito N, Sakamoto K, Itoyama Y, Tanji J. Activity in the lateral prefrontal cortex reflects multiple steps of future events in action plans. Neuron. 2006 ;50:631-41.
Shima K, Isoda M, Mushiake H, Tanji J. Categorization of behavioural sequences in the prefrontal cortex.Nature. 2007 445:315-8.
Transfer of memory trace of motor learning accompanied with memory acquisition and consolidation
Most of our motor skill is acquired through learning. Although the cerebellum is well known as the critical site for motor learning, its exact role in the acquisition and storage of motor memory is a subject of long-lasting debate. Two different views are proposed based on the experimental observations of the adaptation of ocular reflexes. One is that
the motor memory is formed within the cerebellar cortex by long-term depression (LTD) of parallel fiber-Purkinje cell synapses, and the other is that the motor memory is formed within cerebellar/vestibular nuclei using signals mediating through the cerebellar cortex. We examined these two views using adaptation paradigms of horizontal optokinetic response (HOKR) eye movement in mice. One hour of the exposure of the mice to the rapid screen oscillation induced an increase in the gains of the HOKR that declined within 24h. However, when 1h of such training was given successively for a week, a long-term increase occurred in the gains of the HOKR, which continued for 2-3 weeks. We examined the role of the cerebellar flocculus and LTD in these short (day-long) and long (week-long) -term adaptations. We revealed by pharmacological and electrophysiological experiments that the memory trace of day-long adaptation is located within the cerebellar flocculus, while that of week-long adaptation is maintained in the vestibular nuclei where the flocculus issues its outputs. We further revealed that LTD plays a critical role for both the day- and week-long adaptations. These results suggest that the trace of motor memory is initially acquired in the cerebellar cortex, and later transferred to cerebellar/vestibular nuclei for consolidation. LTD seems to play an
essential role in both the acquisition and consolidation of motor memory.
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New York: McGraw-Hill.