Yasuo's interest is in the neural basis of learning and memory. He would like to answer such questions as which brain area is involved in acquiring new information, and how the newly learned information is stored by neurons. Humans often perform the same motor action and behavioral procedure repeatedly, and these acts become so routine that we carry them out almost without conscious effort. Much evidence suggests that the striatum and its related neural circuitry are preferentially involved in this habit learning, but little was known about the forms of neural representation underlying such learning.
In Yasuo's recent study, the team chose chronic ensemble recording with multiple tetrodes (electrodes with four recording channels) to monitor simultaneously the activity of 30-50 striatal neurons in the freely moving subject during acquisition and performance of a procedural learning task in a T-maze. In this task, subjects are trained to move forward when the start gate opens and to turn right or left, as instructed by two auditory cues, in order to obtain a food reward at the goal of the maze.
The research team has found striking changes in the task-related responses of neurons in the sensorimotor region of the striatum. At the beginning of training, many neurons in this area increased their firing frequencies during turning at the choice point of the maze. However, with training, units showing the turn-related response decreased significantly. Instead, there were significant increases in units that increased or decreased discharges in relation to the opening of the start-gate or initiation of locomotion (start-related response) and to reaching the goal area (goal-related response).
These results suggest that the neural representation of behaviors necessary to perform this learning task undergoes transformation during acquisition, and that the new pattern of representation that develops as a result of learning emphasizes the beginning and the end of the automatized behavioral procedure.
In future studies, Yasuo plans to examine what these acquired patterns of neuronal responses represent, how the neuronal network processes and stores task-related information, and how the striatum interacts with other connected brain structures in developing and maintaining such patterns.
DeCoteau WE, Thorn C, Gibson DJ, Courtemanche R, Mitra P, Kubota Y, Graybiel AM. Learning-related coordination of striatal and hippocampal theta rhythms during acquisition of a procedural maze task. Proc Natl Acad Sci U S A. 2007 Mar 27;104(13):5644-9.
Decoteau WE, Thorn CA, Gibson DJ, Courtemanche R, Mitra P, Kubota Y, Graybiel AM.Oscillations of local field potentials in the rat dorsal striatum during spontaneous and instructed behaviors. J Neurophysiol. 2007 Feb 28
Barnes TD, Kubota Y, Hu D, Jin DZ, Graybiel AM.Activity of striatal neurons reflects dynamic encoding and recoding of procedural memories. Nature. 2005 Oct 20;437(7062):1158-61.
Smith AC, Frank LM, Wirth S, Yanike M, Hu D, Kubota Y, Graybiel AM, Suzuki WA, Brown EN.Dynamic analysis of learning in behavioral experiments. J Neurosci. 2004 Jan 14;24(2):447-61.
Jog MS, Connolly CI, Kubota Y, Iyengar DR, Garrido L, Harlan R, Graybiel AM. Tetrode technology: advances in implantable hardware, neuroimaging, and data analysis techniques. J Neurosci Methods. 2002 Jun 30;117(2):141-52.
Jog MS, Kubota Y, Connolly CI, Hillegaart V, Graybiel AM. Building neural representations of habits.