Contrasting Interpretations of the Nonuniform Distribution of Preferred Directions Within Primary Motor Cortex
2007; American Physiological Society; Volume: 97; Issue: 6 Linguagem: Inglês
10.1152/jn.00032.2007
ISSN1522-1598
AutoresIsaac Kurtzer, Troy M. Herter,
Tópico(s)EEG and Brain-Computer Interfaces
ResumoLETTERS TO THE EDITORContrasting Interpretations of the Nonuniform Distribution of Preferred Directions Within Primary Motor CortexIsaac Kurtzer, and Troy M. HerterIsaac Kurtzer, and Troy M. HerterPublished Online:01 Jun 2007https://doi.org/10.1152/jn.00032.2007MoreSectionsPDF (31 KB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInEmailWeChat to the editor: A recent paper by Georgopoulos and colleagues (Naselaris et al. 2006) revisits the influential and controversial issue of population coding within primary motor cortex (M1). Although researchers uniformly recognize that neural activity in M1 often covaries with the direction of limb movement, it is unclear whether these “preferred directions” reflect a high-level representation of hand motion (e.g., Georgopoulos et al. 1986; Graziano et al. 2002; Schwartz and Moran 1999), a low-level representation of the musculoskeletal apparatus (e.g., Mussa-Ivaldi 1988; Scott 1997; Sergio and Kalaska 1998; Todorov 2000), or a mixture of both (e.g., Crutcher and Alexander 1990; Hatsopoulos et al. 2006; Kakei et al. 1999).Georgopoulos and colleagues contribute to this effort with three observations on neural tuning during three-dimensional (3D) reaching: 1) the most common “preferred directions” are forward/up and backward/down hand movements, 2) the alignment between hand motion and the combined activity of the neural population varies with reaching direction, and 3) the magnitude of this population signal also varies with reaching direction. The authors interpret these findings as an augmented representation or “hyperacuity” of particular spatial directions within the framework of high-level planning. They further hypothesize that forward/backward reaching movements are more frequent and thus engage practice-dependent plasticity mechanisms.An alternative interpretation is that the biased distribution of preferred hand directions is evidence against the hand-based theory and evidence for a low-level representation. In fact, this conclusion was reached several years earlier based on the same three global patterns of M1 activity (Scott et al. 2001), a similarity and contrast overlooked by Georgopoulos and colleagues. Whereas the recent study used a 3D paradigm, Scott and colleagues studied reaching movements that involved just flexion and extension of the shoulder and elbow. The strength of this planar paradigm is the ability to compare neural activity to measured mechanical variables such as joint motion and joint torque. Thereby, they demonstrate that the neural bias is lawfully related to nonuniformities in the limb's complex mechanics and likely reflects the impact of muscle shortening on muscle force; a similar nonunifomity of preferred directions has since been confirmed in arm muscles (Kurtzer et al. 2006).It should be noted that Georgopoulos and colleagues were unlikely to reach this conclusion relating neural activity to low-level representations due to the limitation of their paradigm, i.e., only 3D hand motion is recorded, whereas the arm's seven degrees of freedom can contribute to its motion. This difference in paradigms helps explain how the two groups arrive at substantially different conclusions from the same results. The reader is left to decide between these dramatically different interpretations of the same basic result.REFERENCESCrutcher and Alexander 1990 Crutcher MD, Alexander GE. 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Comparison of onset time and magnitude of activity for proximal arm muscles and motor cortical cells before reaching movements. J Neurophysiol 77: 1016–1022, 1997.Link | ISI | Google ScholarScott et al. 2001 Scott SH, Gribble PL, Graham KM, Cabel DW. Dissociation between hand motion and population vectors from neural activity in motor cortex. Nature 413: 161–165, 2001.Crossref | PubMed | ISI | Google ScholarSergio and Kalaska 1998 Sergio LE, Kalaska JF. Changes in the temporal pattern of primary motor cortex activity in a directional isometric force versus limb movement task. J Neurophysiol 80: 1577–1583, 1998.Link | ISI | Google ScholarTodorov 2000 Todorov E. Direct cortical control of muscle activation in voluntary arm movements: a model. Nat Neurosci 3: 391–398, 2000.Crossref | PubMed | ISI | Google ScholarWu and Hatsopoulos 2006 Wu W, Hatsopoulos N. Evidence against a single coordinate system representation in the motor cortex. Exp Brain Res 175: 197–210, 2006.Crossref | PubMed | ISI | Google ScholarAUTHOR NOTESAddress for reprint requests and other correspondence: I. Kurtzer or Troy Herter, Centre for Neuroscience Studies, Botterell Hall, Rm 236, Queen's University, Kingston, Ontario, K7L 3N6, Canada (E-mail. [email protected]; [email protected]) Download PDF Previous Back to Top Next FiguresReferencesRelatedInformationCited ByIndirect, referent control of motor actions underlies directional tuning of neuronsAnatol G. Feldman28 February 2019 | Journal of Neurophysiology, Vol. 121, No. 3Neural Population Dynamics during Reaching Are Better Explained by a Dynamical System than Representational Tuning4 November 2016 | PLOS Computational Biology, Vol. 12, No. 11Learning with Slight Forgetting Optimizes Sensorimotor Transformation in Redundant Motor Systems28 June 2012 | PLoS Computational Biology, Vol. 8, No. 6Techniques for extracting single-trial activity patterns from large-scale neural recordingsCurrent Opinion in Neurobiology, Vol. 17, No. 5Reply to Kurtzer and HerterApostolos P. Georgopoulos, Thomas Naselaris, Hugo Merchant, and Bagrat Amirikian1 June 2007 | Journal of Neurophysiology, Vol. 97, No. 6 More from this issue > Volume 97Issue 6June 2007Pages 4390-4390 Copyright & PermissionsCopyright © 2007 by the American Physiological Societyhttps://doi.org/10.1152/jn.00032.2007PubMed17553955History Published online 1 June 2007 Published in print 1 June 2007 Metrics
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