Alex Cayco Gajic Journal Club 10/29/13. How does motor cortex generate muscle activity?...
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Transcript of Alex Cayco Gajic Journal Club 10/29/13. How does motor cortex generate muscle activity?...
![Page 1: Alex Cayco Gajic Journal Club 10/29/13. How does motor cortex generate muscle activity? Representational perspective: Muscle activity or abstract trajectory.](https://reader038.fdocuments.us/reader038/viewer/2022102923/5518a2af550346991f8b4940/html5/thumbnails/1.jpg)
Alex Cayco GajicJournal Club 10/29/13
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How does motor cortex generate muscle activity?
Representational perspective:
• Muscle activity or abstract trajectory parameters? (e.g. hand velocity)
• Focus on ‘code’ in single neurons
![Page 3: Alex Cayco Gajic Journal Club 10/29/13. How does motor cortex generate muscle activity? Representational perspective: Muscle activity or abstract trajectory.](https://reader038.fdocuments.us/reader038/viewer/2022102923/5518a2af550346991f8b4940/html5/thumbnails/3.jpg)
An epic, twenty-year battle was fought over the cortical representation of movement. Do motor cortex neurons represent the direction of the hand during reaching, or do they represent other features of movement such as joint rotation or muscle output?
Graziano 2011
Criticism of the representational approach
The role of the motor system is to produce movement, not to describe it.
Cisek 2006
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How does motor cortex generate muscle activity?
Representational perspective:
• Muscle activity or abstract trajectory parameters? (e.g. hand velocity)
• Focus on ‘code’ in single neurons
Dynamical systems perspective:
• How can cortex flexibly generate such a large repertoire of movements?
• Focus on basis sets/ mixed signals, network properties
![Page 5: Alex Cayco Gajic Journal Club 10/29/13. How does motor cortex generate muscle activity? Representational perspective: Muscle activity or abstract trajectory.](https://reader038.fdocuments.us/reader038/viewer/2022102923/5518a2af550346991f8b4940/html5/thumbnails/5.jpg)
A few equations
• Representational view:rn(t) = fn(param1(t),param2(t),…)
• Dynamical systems perspective:• Neural responses muscle movement:
m(t) = G[r(t)]But dimensionality of m << dimensionality of r, so G is probably not invertible
• Dynamical system for population activity: τ r’(t) = h(r(t)) + u(t)
• Dimensionality reduction techniques will be important to find robust, redundant activity patterns
![Page 6: Alex Cayco Gajic Journal Club 10/29/13. How does motor cortex generate muscle activity? Representational perspective: Muscle activity or abstract trajectory.](https://reader038.fdocuments.us/reader038/viewer/2022102923/5518a2af550346991f8b4940/html5/thumbnails/6.jpg)
Voluntary movements are “prepared”
Random delay periodChurchland et al. 2006
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Voluntary movements are “prepared”
• RT decreases with delay period, indicating “preparation”
Churchland et al. 2006
![Page 8: Alex Cayco Gajic Journal Club 10/29/13. How does motor cortex generate muscle activity? Representational perspective: Muscle activity or abstract trajectory.](https://reader038.fdocuments.us/reader038/viewer/2022102923/5518a2af550346991f8b4940/html5/thumbnails/8.jpg)
Voluntary movements are “prepared”
• RT decreases with delay period, indicating “preparation”
• Variety of complex single-neuron responses
Churchland et al. 2006
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What is preparatory activity?Representational view
• Hypothesis: preparatory activity is the subthreshold form of movement activity
Churchland et al. 2010a
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What is preparatory activity?Representational view
• Hypothesis: preparatory activity is the subthreshold form of movement activity
Churchland et al. 2010a
![Page 11: Alex Cayco Gajic Journal Club 10/29/13. How does motor cortex generate muscle activity? Representational perspective: Muscle activity or abstract trajectory.](https://reader038.fdocuments.us/reader038/viewer/2022102923/5518a2af550346991f8b4940/html5/thumbnails/11.jpg)
What is preparatory activity?Representational view
• Hypothesis: preparatory activity is the subthreshold form of movement activity
Churchland et al. 2010a
![Page 12: Alex Cayco Gajic Journal Club 10/29/13. How does motor cortex generate muscle activity? Representational perspective: Muscle activity or abstract trajectory.](https://reader038.fdocuments.us/reader038/viewer/2022102923/5518a2af550346991f8b4940/html5/thumbnails/12.jpg)
What is preparatory activity?Representational view
• Hypothesis: preparatory activity is the subthreshold form of movement activity
• Reality: preparatory & movement tuning are uncorrelated on average
Churchland et al. 2010a
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What is preparatory activity tuned for?
Churchland et al. 2010a
Leave out one condition (direction), use linear regression to predict left-out preparatory firing rate from a set of “preferred directions”.
dimensionality
PCA analysis:
• Perimovement: activity of other neurons
• Kinematic: position, velocity, acceleration
• EMG: activity for multiple muscles
Best performance: from whole population dynamics.
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What is preparatory activity?Dynamical systems view
• Hypothesis: preparatory activity brings population dynamical state to an initial value that produces correct motion with minimal reaction time.
Churchland et al. 2010b
• Reduction in variability across different trials as states converge to muscle activation (FF)
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What is preparatory activity?Dynamical systems view
• Hypothesis: preparatory activity brings population dynamical state to an initial value that produces correct motion with minimal reaction time.
Churchland et al. 2010b
![Page 16: Alex Cayco Gajic Journal Club 10/29/13. How does motor cortex generate muscle activity? Representational perspective: Muscle activity or abstract trajectory.](https://reader038.fdocuments.us/reader038/viewer/2022102923/5518a2af550346991f8b4940/html5/thumbnails/16.jpg)
What is preparatory activity?Dynamical systems view
• Hypothesis: preparatory activity brings population dynamical state to an initial value that produces correct motion with minimal reaction time.
Churchland et al. 2010b
![Page 17: Alex Cayco Gajic Journal Club 10/29/13. How does motor cortex generate muscle activity? Representational perspective: Muscle activity or abstract trajectory.](https://reader038.fdocuments.us/reader038/viewer/2022102923/5518a2af550346991f8b4940/html5/thumbnails/17.jpg)
What is preparatory activity?Dynamical systems view
• Hypothesis: preparatory activity brings population dynamical state to an initial value that produces correct motion with minimal reaction time.
Churchland et al. 2010b
![Page 18: Alex Cayco Gajic Journal Club 10/29/13. How does motor cortex generate muscle activity? Representational perspective: Muscle activity or abstract trajectory.](https://reader038.fdocuments.us/reader038/viewer/2022102923/5518a2af550346991f8b4940/html5/thumbnails/18.jpg)
Convergence of trajectories• Reduction in variance comes from convergence of
trajectories during motor preparation
Churchland et al. 2010b
Outlier (monkey hesitated)
Covariance ellipses
10-D PCA
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Convergence of trajectories• Reduction in variance comes from convergence of
trajectories during motor preparation
Churchland et al. 2010b
Outlier (monkey hesitated)
• Prediction: perturbing initial states near go cue should increase RT
Covariance ellipses
10-D PCA
![Page 20: Alex Cayco Gajic Journal Club 10/29/13. How does motor cortex generate muscle activity? Representational perspective: Muscle activity or abstract trajectory.](https://reader038.fdocuments.us/reader038/viewer/2022102923/5518a2af550346991f8b4940/html5/thumbnails/20.jpg)
Preparation & response time
Churchland & Shenoy 2007a
• Use subthreshold microstimulation to perturb prepatory activity
• No change in wave profile, change in RT only when perturbation occurs at go cue
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Preparation & response time
• Use subthreshold microstimulation to perturb prepatory activity
• No change in wave profile, change in RT only when perturbation occurs at go cue
• Change in RT due to preparatory state – less dramatic in M1, doesn’t exist in saccadic RT
Churchland & Shenoy 2007a
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Preparation & response time
Afshar et al 2011
• corr(alpha,RT) ?
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Preparation & response time
Afshar et al 2011
• Farther along mean neural trajectory smaller RT
• corr(alpha,RT) < 0
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PMd neural responses are bizarre
Churchland et al. 2010a
• Tuning differs between preparatory & perimovement periods• Response are complex and multiphasic• Responses of different neurons are heterogeneous• Activity fluctuates longer than movement scale
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Low-dimensional activity is rotational
• In low-dimensionality projections, trajectories rotate with phase set by preparatory state (captures ~28% variance)
• However, the reaches were not overtly rhythmic
• Brief sinusoidal oscillations form a basis set for more complex patterns
Churchland et al. 2012
![Page 26: Alex Cayco Gajic Journal Club 10/29/13. How does motor cortex generate muscle activity? Representational perspective: Muscle activity or abstract trajectory.](https://reader038.fdocuments.us/reader038/viewer/2022102923/5518a2af550346991f8b4940/html5/thumbnails/26.jpg)
Neural population responses are rotational
Churchland et al. 2012
![Page 27: Alex Cayco Gajic Journal Club 10/29/13. How does motor cortex generate muscle activity? Representational perspective: Muscle activity or abstract trajectory.](https://reader038.fdocuments.us/reader038/viewer/2022102923/5518a2af550346991f8b4940/html5/thumbnails/27.jpg)
Kinematic/EMG data are not
Churchland et al. 2012
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What is jPCA?
• X = (n)x(ct) matrix• PCA to reduce to Xred = (k)x(ct)• Fit Xred’ = MXred, Xred’ = MskewXred
using linear regression• V1, V2 conjugate eigenvectors of
Mskew
• jPC1 = V1+V2
• jPC2 = j(V1-V2)• Project Xred onto jPC1, jPC2
Churchland et al. 2012
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Conclusions
• Dynamical systems approach gives insight into movement without making assumptions about single-neuron tuning.
• “Preparation” funnels neural trajectories to achieve fast movement without minimal variation.
• Preparatory state predicts both RT and trial-to-trial variability.
• Rotational PMd firing rate dynamics form a basis for more complex muscular activity.