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Reposted by Mehrdad Kashefi

Jonathan A. Michaels @jonathanamichaels.bsky.social · 7d

The neural control & computation lab is recruiting!

If you're interested in using large-scale neural population recordings to study how the brain learns to produce complex and flexible behaviours, please get in touch.

www.ncclab.ca

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Reposted by Mehrdad Kashefi

Paul Gribble 🇨🇦 @gribblelab.org · 26d

This week's sensorimotor superlab reading list is out https://superlab.ca/posts/2025-09-12-list303.html @andpru.bsky.social @diedrichsenjorn.bsky.social @gribblelab.org #neuroskyence #psychscisky #Sensorimotor

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Reposted by Mehrdad Kashefi

Jörn Diedrichsen @diedrichsenjorn.bsky.social · 28d

Variance partitioning is used to quantify the overlap of two models. Over the years, I have found that this can be a very confusing and misleading concept. So we finally we decided to write a short blog to explain why.
@martinhebart.bsky.social @gallantlab.org
diedrichsenlab.org/BrainDataSci...

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Reposted by Mehrdad Kashefi

Sam McDougle @actlab.bsky.social · Sep 8

New preprint from the lab! 🧠
Led by Juliana Trach, w/ Sophia Ou

Using fMRI, we discovered evidence for time-sensitive reward prediction errors (RPEs) in the human cerebellum.

Builds on, and extends, recent work in both rodents and NHPs

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Reposted by Mehrdad Kashefi

Jörn Diedrichsen @diedrichsenjorn.bsky.social · Sep 8

Exited to share tomorrow new updates on trying to figure out how the neocortex and cerebellum talk to each other. Work by @carobellum.bsky.social, Ali Shabazi, and others in the lab!

Reza Shadmehr @rezashadmehr.bsky.social · Sep 4

To understand cortico-cerebellar connectivity in humans, the usual approach is to exploit the correlations of functional brain imaging signals during rest.
In this talk, Jorn Diedrichsen will present results suggesting that a better approach is to measure co-activation during specific tasks.

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Mehrdad Kashefi @mkashefi.bsky.social · Sep 6

Thanks Josh!

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Mehrdad Kashefi @mkashefi.bsky.social · Sep 6

Thanks Mahdiyar!

Mehrdad Kashefi @mkashefi.bsky.social · Sep 6

Thanks Harrison!

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Mehrdad Kashefi @mkashefi.bsky.social · Sep 6

Thanks for reading 🙏 The paper also covers recordings from SMA, pre-SMA, dlPFC & GPi.
Full details here ⬇️ www.biorxiv.org/content/10.1...
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Compositional neural dynamics during reaching

The complex mechanics of the arm make the neural control of reaching inherently posture dependent. Because previous reaching studies confound reach direction with final posture, it remains unknown how...

www.biorxiv.org

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Mehrdad Kashefi @mkashefi.bsky.social · Sep 6

Conclusion: Motor cortex dynamics are compositional. They simultaneously:
- generate movement
- maintain an internal representation of posture
- track task progress
9/10

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Mehrdad Kashefi @mkashefi.bsky.social · Sep 6

Modeling: Using modular RNNs, we asked what’s required for this compositional structure to emerge. It turns out this solution is common whenever the effector is complex enough to demand posture-dependent control policies. 8/10

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Mehrdad Kashefi @mkashefi.bsky.social · Sep 6

3️⃣ A condition-independent shift dimension: a trajectory reflecting trial progression, unfolding similarly across all movements, regardless of direction or posture. 7/10

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Mehrdad Kashefi @mkashefi.bsky.social · Sep 6

2️⃣ Rotational dynamics: transitions linking posture-specific fixed points.These rotations were systematic—similar rotations produced similar reach directions—and their projection continuously updated posture. 6/10

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Mehrdad Kashefi @mkashefi.bsky.social · Sep 6

Key finding: High-density recordings from M1 & PMd revealed a compositional neural geometry with 3 components. 1️⃣ A posture subspace: fixed points for each target, visited whenever the arm rested at that location before or after a reach. 5/10

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Mehrdad Kashefi @mkashefi.bsky.social · Sep 6

Our approach: We trained monkeys to reach between all pairs of 5 targets. Each target was a start point on some trials and an end point on others. This design let us dissociate posture representations from movement dynamics. 4/10

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Mehrdad Kashefi @mkashefi.bsky.social · Sep 6

Why this problem exists: Most insights come from center-out tasks, where all movements start from one spot. Here, reach direction and final posture are always correlated—making it impossible to separate movement dynamics from posture encoding. 3/10

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Mehrdad Kashefi @mkashefi.bsky.social · Sep 6

The problem: Moving your arm to grab coffee requires different muscle commands depending on where your arm starts. We know the brain must incorporate posture when planning movement—but how neural dynamics achieve this remains unclear. 2/10

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Mehrdad Kashefi @mkashefi.bsky.social · Sep 6

Excited to share my latest work with @jonathanamichaels.bsky.social @diedrichsenjorn.bsky.social & @andpru.bsky.social!
We asked: How does the motor cortex account for arm posture when generating movement?
Paper 👉 www.biorxiv.org/content/10.1...
1/10

Compositional neural dynamics during reaching

The complex mechanics of the arm make the neural control of reaching inherently posture dependent. Because previous reaching studies confound reach direction with final posture, it remains unknown how...

www.biorxiv.org

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Mehrdad Kashefi @mkashefi.bsky.social · Jul 9

Thanks! This is highly relevant to our work.

Mehrdad Kashefi @mkashefi.bsky.social · Jul 8

If this doesn't solve the issue send me an email. Happy to chat more about it!

Mehrdad Kashefi @mkashefi.bsky.social · Jul 8

If that were the case, I would expect this representation to transfer across effectors—especially when the visual sequence remains identical. However, this isn’t what we observe in our data (see Experiment 2 in the paper).

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Mehrdad Kashefi @mkashefi.bsky.social · Jul 8

Hi Alfred Nobel! Thanks for your interest! If I understand you correctly, you're suggesting that participants might form a purely cognitive representation of the sequence "shape."

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Reposted by Mehrdad Kashefi

Sebastian Lehmann @lehmannsj.bsky.social · Apr 29

We're excited to share our new paper: “cTBS of prefrontal cortex in the behaving macaque: no evidence for within-target inhibition or cross-hemisphere disinhibition of neural activity”
tinyurl.com/cTBSPFCNHP
w/ @brian-corneil.bsky.social

What did we find? Mostly... what we didn’t! 🧵

tinyurl.com

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Mehrdad Kashefi @mkashefi.bsky.social · Apr 26

✋

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Mehrdad Kashefi @mkashefi.bsky.social · Mar 27

Heading to #cosyne2025 ?

We're presenting new data exploring the geometry of neural dynamics in M1, PMd, PFC, SMA, and GPi during reaching movements with varying start locations, directions, and extents.

Find me at Poster Session 3-091 — or anytime before or after!

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