Co-Planar Stereotaxic Atlas of the Human Brain—3-Dimensional Proportional System: An Approach to Cerebral Imaging, J. Talairach, P. Tournoux. Georg Thieme Verlag, New York (1988), 122 pp., 130 figs. DM 268

I have developed "tennis elbow" from lugging this book around the past four weeks, but it is worth the pain, the effort, and the aspirin. It is also worth the (relatively speaking) bargain price. Including appendixes, this book contains 894 pages of text. The entire panorama of the neural sciences is surveyed and examined, and it is comprehensive in its scope, from genomes to social behaviors. The editors explicitly state that the book is designed as "an introductory text for students of biology, behavior, and medicine," but it is hard to imagine any audience, interested in any fragment of neuroscience at any level of sophistication, that would not enjoy this book. The editors have done a masterful job of weaving together the biologic, the behavioral, and the clinical sciences into a single tapestry in which everyone from the molecular biologist to the practicing psychiatrist can find and appreciate his or

Principles of Neural Science

Prospective Cohort Study

http://science.sciencemag.org/content/sci/201/4359/899.2.full.pdf

Phenomenology of perception.

A free-energy principle has been proposed recently that accounts for action, perception and learning. This Review looks at some key brain theories in the biological (for example, neural Darwinism) and physical (for example, information theory and optimal control theory) sciences from the free-energy perspective. Crucially, one key theme runs through each of these theories — optimization. Furthermore, if we look closely at what is optimized, the same quantity keeps emerging, namely value (expected reward, expected utility) or its complement, surprise (prediction error, expected cost). This is the quantity that is optimized under the free-energy principle, which suggests that several global brain theories might be unified within a free-energy framework.

/pdf/the-free-energy-principle-a-unified-brain-theory-3vz1twg7nv.pdf

The free-energy principle: a unified brain theory?

It has long been of interest what the contribution of pathological synergies is to abnormal motor control of the arm after stroke. The flexor synergy is defined as unwanted co-activation of flexion at the shoulder and elbow joints. Here we used a video-based, marker-less 3D pose-estimation kinematic model to examine two reaching tasks with different requirements for elbow flexion. Twenty-eight sub-acute (2-12 weeks) post-stroke subjects and sixteen healthy controls performed both a cup to mouth task, requiring shoulder and elbow flexion (within flexor synergy), and a reaching task, requiring shoulder flexion and elbow extension (outside of flexor synergy). Using kinematic analysis of the hand and of elbow/shoulder joint angles, we assessed both overall task performance and intrusion of pathological synergies. Motor impairment, strength and spasticity were measured using established clinical scales. Performance in both tasks was impaired to a similar degree in the patients compared to controls. This lack of performance difference for the in- vs. out-of-flexor synergy tasks was consistent with our finding of no evidence for intrusion of a flexor synergy in the reaching task. Specifically, for the reaching task there was no difference between patients and controls either in time spent within-movement in flexor synergy or in the correlation between shoulder and elbow angles when the shoulder was flexing. A regression analysis indicated that the only significant predictor of poor task performance was degree of weakness. Notably, even though we found no kinematic evidence for post-stroke intrusive flexor synergies, the Fugl-Meyer Assessment (FMA), which was devised to quantify post-stroke synergies, was markedly abnormal. This seeming contradiction is resolved by the observation that abnormal coupling at the shoulder and elbow can occur due to weakness alone, and it is this “synergy mimic” that leads to a low FMA score. The finding that FMA can be abnormal for two qualitatively distinct forms of impaired inter-joint coordination has implications for the interpretation of longitudinal studies that use this single measure. In the sub-acute stage of stroke, intrusion of abnormal synergies is not the reason for impaired reaching.

/pdf/intrusion-of-pathological-synergies-does-not-explain-1d2m2vq7.pdf

Intrusion of pathological synergies does not explain impaired 3D arm movements in subacute stroke

During learning of novel motor sequences, practice leads to the consolidation of hierarchical structures, namely motor chunks, facilitating the accurate execution of sequences at increasing speeds. Recent studies show that such hierarchical structures are largely represented upstream of the primary motor cortex in the motor network, suggesting their function to be more related to the encoding, storage, and retrieval of sequences rather than their sole execution. We isolated different components of motor skill acquisition related to the consolidation of spatiotemporal features and followed their evolution over training. We found that optimal motor skill acquisition relies on the storage of the spatial features of the sequence in memory, followed by the optimization of its execution and increased execution speeds (i.e., a shift in the speed-accuracy trade-off) early in training, supporting the model proposed by Hikosaka in 1999. Contrasting the dynamics of these components during ageing, we identified less-than-optimal mechanisms in older adults explaining the observed differences in performance. We applied noninvasive brain stimulation in an attempt to support the aging brain to compensate for these deficits. The present study found that anodal direct current stimulation applied over the motor cortex restored the mechanisms involved in the consolidation of spatial features, without directly affecting the speed of execution of the sequence. This led older adults to sharply improve their accuracy, resulting in an earlier yet gradual emergence of motor chunks. The results suggest the early storage of the sequence in memory, largely independent of motor practice, is crucial for an optimal motor acquisition and retrieval of this motor behavior. Nevertheless, the consolidation of optimal temporal patterns, detected as motor chunks at a behavioral level, is not a direct consequence of storing the sequence elements, but rather of motor practice.

https://biorxiv.org/content/10.1101/2021.12.01.470563v1.full.pdf

John W. Krakauer

Papers

Intrusion of pathological synergies does not explain impaired 3D arm movements in subacute stroke

Black-box testing in motor sequence learning

StudyRotations and Gains for Reaching: A PET Differential Cortical and Subcortical Activations in

preparation and execution The roles of monkey M1 neuron classes in movement

performance or error adaptation and depends on learning rather than Corticospinal excitability is enhanced after visuomotor