Possible Origins of the Complex Topographic Organization of Motor Cortex: Reduction of a Multidimensional Space onto a Two-Dimensional Array

Aflalo, Tyson; Graziano, Michael S. A.

doi:10.1523/jneurosci.0768-06.2006

Cited by 111 publications

(82 citation statements)

References 35 publications

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“…Given the high correlation between the statistics of eye and arm movements, similar activations in brain areas governing the movements of these effectors might well be expected. Interestingly, a recent paper has made a similar suggestion regarding encoding in motor cortex, namely that representations of different effectors are overlapping because the animal uses those effectors together in normal behavior (Aflalo and Graziano, 2006a). At the same time, although arm movements are usually correlated with eye movements, we do occasionally dissociate these effectors.…”

Section: Separability Of Saccades and Reaching: Efficient Coding Consmentioning

confidence: 57%

Specificity of Human Cortical Areas for Reaches and Saccades

Levy¹,

Schluppeck²,

Heeger³

et al. 2007

J. Neurosci.

131

123

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Electrophysiological studies in monkeys have identified effector-related regions in the posterior parietal cortex (PPC). The lateral intraparietal area, for example, responds preferentially for saccades, whereas the parietal reach region responds preferentially for arm movements. However, the degree of effector selectivity actually observed is limited; each area contains neurons selective for the nonpreferred effector, and many neurons in both areas respond for both effectors. We used functional magnetic resonance imaging to assess the degree of effector preference at the population level, focusing on topographically organized regions in the human PPC [visual area V7, intraparietal sulcus 1 (IPS1), and IPS2]. An event-related design adapted from monkey experiments was used. In each trial, an effector cue preceded the appearance of a spatial target, after which a Go signal instructed subjects to produce the specified movement with the specified effector. Our results show that the degree of effector specificity is limited in many cortical areas and transitions gradually from saccade to reach preference as one moves through the hierarchy of areas in the occipital, parietal, and frontal cortices. Saccade preference was observed in visual cortex, including early areas and V7. IPS1 exhibited balanced activation to saccades and reaches, whereas IPS2 showed a weak but significant preference for reaches. In frontal cortex, areas near the central sulcus showed a clear and absolute preference for reaches, whereas the frontal eye field showed little or no effector selectivity. Although these results contradict many theoretical conclusions about effector specificity, they are compatible with the complex picture arising from electrophysiological studies and also with previous imaging studies that reported mostly overlapping saccade-and arm-related activation. The results are also compatible with theories of efficient coding in cortex.

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Section: Separability Of Saccades and Reaching: Efficient Coding Consmentioning

confidence: 57%

Specificity of Human Cortical Areas for Reaches and Saccades

Levy¹,

Schluppeck²,

Heeger³

et al. 2007

J. Neurosci.

131

123

View full text Add to dashboard Cite

show abstract

“…The purpose of the model (Aflalo and Graziano 2006) was to begin with a set of movement dimensions that we believed to be relevant to the monkey motor cortex, to perform a dimensionality reduction to represent those movement dimensions on a two-dimensional cortical sheet, and to compare the resultant map in the model to the actual maps obtained in the monkey brain.…”

Section: A Model Of the Lateral Motor Cortexmentioning

confidence: 99%

“…We then describe some alternative organizations that have been proposed. Finally, we describe a formal model of the topographic organization of the precentral gyrus (Aflalo and Graziano 2006). In this model, several different dimensions of movement compete for space on the two-dimensional cortical sheet.…”

mentioning

confidence: 99%

Rethinking Cortical Organization

Graziano

Aflalo

2007

Neuroscientist

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One way to understand the topography of the cerebral cortex is that “like attracts like.” The cortex is organized to maximize nearest neighbor similarity. This principle can explain the separation of the cortex into discrete areas that emphasize different information domains. It can also explain the maps that form within cortical areas. However, because the cortex is two-dimensional, when a parameter space of much higher dimensionality is reduced onto the cortical sheet while optimizing nearest neighbor relationships, the result may lack an obvious global ordering into separate areas. Instead, the topography may consist of partial gradients, fractures, swirls, regions that resemble separate areas in some ways but not others, and in not a lack of topographic maps but an excess of maps overlaid on each other, no one of which seems to be entirely correct. Like a canvas in a gallery of modern art that no two observers interpret the same way, this lack of obvious ordering of high-dimensional spaces onto the cortex might then result in some scientific controversy over the true organization. In this review, the authors suggest that at least some sectors of the cortex do not have a simple global ordering and are better understood as a result of a reduction of a high-dimensional space onto the cortical sheet. The cortical motor system may be an example of this phenomenon. The authors discuss a model of the lateral motor cortex in which a reduction of many parameters onto a simulated cortical sheet results in a complex topographic pattern that matches the actual monkey motor cortex in surprising detail. Some of the ambiguities of topography and areal boundaries that have plagued the attempt to systematize the lateral motor cortex are explained by the model. NEUROSCIENTIST the attempt to syste 13(2):138—147, 2007.

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“…One hypothesis that might explain the results of HFLD-ICMS is that the stimulus activates a natural physiological output circuit which is modified by afferent feedback to make it appropriate for the direction of movement needed to achieve a target position relative to the current position of the hand (Graziano et al, 2004;Aflalo and Graziano, 2006a). The natural circuit hypothesis predicts that HFLD-ICMS-evoked EMG responses will be highly dependent on arm posture and joint angle.…”

Section: Introductionmentioning

confidence: 99%

EMG Activation Patterns Associated with High Frequency, Long-Duration Intracortical Microstimulation of Primary Motor Cortex

et al. 2014

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The delivery of high-frequency, long-duration intracortical microstimulation (HFLD-ICMS) to primary motor cortex (M1) in primates produces hand movements to a common final end-point regardless of the starting hand position (Graziano et al., 2002). We have confirmed this general conclusion. We further investigated the extent to which the (1) temporal pattern, (2) magnitude, and (3) latency of electromyographic (EMG) activation associated with HFLD-ICMS-evoked movements are dependent on task conditions, including limb posture. HFLD-ICMS was applied to layer V sites in M1 cortex. EMG activation with HFLD-ICMS was evaluated while two male rhesus macaques performed a number of tasks in which the starting position of the hand could be varied throughout the workspace. HFLD-ICMS-evoked EMG activity was largely stable across all parameters tested independent of starting hand position. The most common temporal pattern of HFLD-ICMS-evoked EMG activity (58% of responses) was a sharp rise to a plateau. The plateau level was maintained essentially constant for the entire duration of the stimulus train. The plateau pattern is qualitatively different from the largely bell-shaped patterns typical of EMG activity associated with natural goal directed movements (Brown and Cooke, 1990; Hoffman and Strick, 1999). HFLD-ICMS produces relatively fixed parameters of muscle activation independent of limb position. We conclude that joint movement associated with HFLD-ICMS occurs as a function of the length-tension properties of stimulus-activated muscles until an equilibrium between agonist and antagonist muscle force is achieved.

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Possible Origins of the Complex Topographic Organization of Motor Cortex: Reduction of a Multidimensional Space onto a Two-Dimensional Array

Cited by 111 publications

References 35 publications

Specificity of Human Cortical Areas for Reaches and Saccades

Specificity of Human Cortical Areas for Reaches and Saccades

Rethinking Cortical Organization

EMG Activation Patterns Associated with High Frequency, Long-Duration Intracortical Microstimulation of Primary Motor Cortex

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