QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

HOME  |   SEARCH  |   ARCHIVE  |   SUBSCRIBE  |   CONTACT  |   HELP

The Journal of Neuroscience, March 1, 2006, 26(9):2487-2498; doi:10.1523/JNEUROSCI.3590-05.2006

This Article Full Text Full Text (PDF) Submit an eLetter Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Web of Science (3) Citing Articles via Google Scholar Google Scholar Articles by Maimon, G. Articles by Assad, J. A. Search for Related Content PubMed PubMed Citation Articles by Maimon, G. Articles by Assad, J. A.

 Previous Article  |  Next Article 

Behavioral/Systems/Cognitive
Parietal Area 5 and the Initiation of Self-Timed Movements versus Simple Reactions

Gaby Maimon and John A. Assad

Department of Neurobiology, Harvard Medical School, Boston, Massachusetts 02115

Correspondence should be addressed to John A. Assad, Department of Neurobiology, Harvard Medical School, Boston, MA 02115. Email: jassad{at}hms.harvard.edu

The timing of action has been studied extensively in reaction-time tasks in which an abrupt sensory stimulus triggers a movement. In these experiments, neurophysiologists have attempted to explain variability in movement time with variability in neuronal activity. However, in natural settings, movements are not usually triggered by abrupt sensory cues. What underlies the timing of action under such circumstances, when movements are uncoupled or only weakly coupled to abrupt events in the external world? We trained monkeys to perform the same arm movement either in direct reaction to a salient visual event, or as a self-timed action, less coupled to any obvious external trigger. Neurons in cortical area 5 exhibited phasic discharge modulations that were generally comparable for both modes of action, with some neurons increasing and others decreasing their firing rates with movement. For self-timed movements, however, there was an additional, slow ramp-up or ramp-down of activity in the few hundred milliseconds before the phasic discharge. These ramping modulations occurred well before any detectable changes in arm-muscle activity and their time course bore a striking resemblance to activity in the putamen preceding self-timed movements, observed previously. Together, the results suggest a possible mechanism for the internal timing of action within the motor system. In this model, reverberant activity in corticobasal-ganglia circuits reaches a threshold level resulting in much larger perimovement discharges within the same network, consequently driving the initiation of action.

Key words: area 5; parietal cortex; motor system; movement initiation; neurophysiology; macaque

---

Received Aug. 24, 2005; revised Dec. 26, 2005; accepted Jan. 17, 2006.

Correspondence should be addressed to John A. Assad, Department of Neurobiology, Harvard Medical School, Boston, MA 02115. Email: jassad{at}hms.harvard.edu

Home  |   Search  |   Archive  |   Subscribe  |   Contact  |   Help