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.

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The free-energy principle: a unified brain theory?

PURPOSE OF REVIEW The aim of this article is to discuss the dynamic nature of cerebrovascular ischemia. RECENT FINDINGS Acute risk factors are superimposed on chronic risk factors to precipitate plaque rupture in myocardial infarction. The interaction between external triggers, such as stress, with internal triggers, such as vasoconstriction, is mediated to a large part by the autonomic nervous system. Numerous algorithms have been developed to describe physiological time-series data, for example heartbeat variability, and reveal complex structure that has diagnostic and prognostic significance. Much of this structure is mediated by the autonomic nervous system. Recent data on stroke triggers, carotid stenosis, transient ischemic attack, and infarct expansion suggest a similar need for detailed physiological measurement and non-linear dynamics in order to understand stroke onset and progression. SUMMARY The picture emerging is that stroke arises as a result of multiple processes with different time constants. The nature and timing of interventions should be tailored to these complex interacting processes. This will require more frequent and varied physiological measurement accompanied by non-linear analytical methods. This new approach, which stresses complex within-subject measurements, will likely make 'one size fits all' solutions to stroke care untenable.

/pdf/the-complex-dynamics-of-stroke-onset-and-progression-1wtqlj1ui9.pdf

The complex dynamics of stroke onset and progression.

The human motor system can rapidly adapt its motor output in response to errors, reducing errors in subsequent movements and thereby improving performance. It remains unclear, however, exactly what mechanism supports this learning. It has been proposed that the implicit adaptation of motor commands in response to errors occurs through updating an internal forward model which predicts the consequences of motor commands. This model can then be used to select appropriate motor commands that will lead to a desired outcome. Alternatively, however, it has been suggested that implicit adaptation might occur by using errors to directly update an underlying policy (often referred to as an inverse model). There is currently little evidence to distinguish between these two possibilities. Here, we exploit the fact that these two different learning architectures make opposing predictions about how people should behave under mirror-reversed visual feedback, and find that peoples9 behavior is consistent with direct policy learning, but not with forward-model-based learning.

https://www.biorxiv.org/content/biorxiv/early/2020/01/23/2020.01.22.914473.full.pdf

Implicit adaptation is driven by direct policy updates rather than forward-model-based learning

We used functional magnetic resonance imaging to investigate whether hemispheral hemodynamic impairment can play an independent role in the functional reorganization of motor-related activity in the brain. Fourteen patients with large vessel occlusion but no infarct performed a simple motor task with the hand contralateral to the occluded vessel. Statistical parametric maps of regional activity were generated to compare the distribution of motor-related activity among patients with that of control subjects. Patients were classified into normal or abnormal cerebral hemodynamics on the basis of intracerebral vasomotor reactivity using transcranial Doppler and carbon dioxide inhalation. Controls and patients with normal vasomotor reactivity showed typical motor activity in contralateral motor areas. When the 9 patients with abnormal vasomotor reactivity were compared with the 14 control subjects in a single analysis, unique motor activation was identified in ipsilateral motor regions in the nonhypoperfused hemisphere. In a confirmatory analysis, blood oxygen level-dependent (BOLD) signal intensity was averaged in prespecified motor regions of interest. A significant group by hemisphere interaction was identified, driven by higher ipsilateral and lower contralateral hemisphere BOLD signal in patients with abnormal vasomotor reactivity compared with controls (F=12.40, P=0.002). The average ipsilateral motor region signal intensity was also significantly higher in the subgroup of patients with abnormal vasoreactivity and no TIA compared with controls (P=0.04). Our results suggest that hemodynamic impairment in one hemisphere, even in the absence of any focal lesion or any symptoms can be associated with a functional reorganization to the opposite hemisphere.

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Hemodynamic impairment as a stimulus for functional brain reorganization.

Practicing a previously unknown motor sequence often leads to the consolidation of motor chunks, which enable its accurate execution at increasing speeds. Recent imaging studies suggest the function of these structures to be more related to the encoding, storage, and retrieval of sequences rather than their sole execution. We found that optimal motor skill acquisition prioritizes the storage of the spatial features of the sequence in memory over its rapid execution early in training, as proposed by Hikosaka in 1999. This process, seemingly diminished in older adults, was partially restored by anodal transcranial direct current stimulation over the motor cortex, as shown by a sharp improvement in accuracy and an earlier yet gradual emergence of motor chunks. These results suggest that the emergence of motor chunks is preceded by the storage of the sequence in memory but is not its direct consequence; rather, these structures depend on, and result from, motor practice.

Dissecting motor skill acquisition: Spatial coordinates take precedence

/pdf/erratum-inside-the-brain-of-an-elite-athlete-the-neural-11aq3okndp.pdf

Erratum: Inside the brain of an elite athlete: The neural processes that support high achievement in sports (Nature Reviews Neuroscience (2009) 10 (585-596))

John W. Krakauer

Papers

The complex dynamics of stroke onset and progression.

Implicit adaptation is driven by direct policy updates rather than forward-model-based learning

Hemodynamic impairment as a stimulus for functional brain reorganization.

Dissecting motor skill acquisition: Spatial coordinates take precedence

Erratum: Inside the brain of an elite athlete: The neural processes that support high achievement in sports (Nature Reviews Neuroscience (2009) 10 (585-596))