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

Thirty years of brain imaging research has converged to define the brain’s default network—a novel and only recently appreciated brain system that participates in internal modes of cognition Here we synthesize past observations to provide strong evidence that the default network is a specific, anatomically defined brain system preferentially active when individuals are not focused on the external environment Analysis of connectional anatomy in the monkey supports the presence of an interconnected brain system Providing insight into function, the default network is active when individuals are engaged in internally focused tasks including autobiographical memory retrieval, envisioning the future, and conceiving the perspectives of others Probing the functional anatomy of the network in detail reveals that it is best understood as multiple interacting subsystems The medial temporal lobe subsystem provides information from prior experiences in the form of memories and associations that are the building blocks of mental simulation The medial prefrontal subsystem facilitates the flexible use of this information during the construction of self-relevant mental simulations These two subsystems converge on important nodes of integration including the posterior cingulate cortex The implications of these functional and anatomical observations are discussed in relation to possible adaptive roles of the default network for using past experiences to plan for the future, navigate social interactions, and maximize the utility of moments when we are not otherwise engaged by the external world We conclude by discussing the relevance of the default network for understanding mental disorders including autism, schizophrenia, and Alzheimer’s disease

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The Brain's Default Network Anatomy, Function, and Relevance to Disease

Information about the basal ganglia has accumulated at a prodigious pace over the past decade, necessitating major revisions in our concepts of the structural and functional organization of these nuclei. From earlier data it had appeared that the basal ganglia served primarily to integrate diverse inputs from the entire cerebral cortex and to "funnel" these influences, via the ventrolateral thalamus, to the motor cortex (Allen & Tsukahara 1974, Evarts & Thach 1969, Kemp & Powell 1971). In particular, the basal

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Parallel Organization of Functionally Segregated Circuits Linking Basal Ganglia and Cortex

This paper describes FieldTrip, an open source software package that we developed for the analysis of MEG, EEG, and other electrophysiological data. The software is implemented as a MATLAB toolbox and includes a complete set of consistent and user-friendly high-level functions that allow experimental neuroscientists to analyze experimental data. It includes algorithms for simple and advanced analysis, such as time-frequency analysis using multitapers, source reconstruction using dipoles, distributed sources and beamformers, connectivity analysis, and nonparametric statistical permutation tests at the channel and source level. The implementation as toolbox allows the user to perform elaborate and structured analyses of large data sets using the MATLAB command line and batch scripting. Furthermore, users and developers can easily extend the functionality and implement new algorithms. The modular design facilitates the reuse in other software packages.

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FieldTrip: open source software for advanced analysis of MEG, EEG, and invasive electrophysiological data

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

We studied the effects of exercise on motor evoked potentials (MEPs) elicited by transcranial magnetic stimulation (TMS) in 18 normal (control) subjects and 11 medication-free patients with cerebellar degeneration. Subjects performed repeated sets of isometric exercise of the extensor carpi radialis muscle until the muscle fatigued (subject became unable to maintain half maximal force). MEPs were recorded before and after each exercise set and for up to 30 minutes after the last set. The mean amplitude of MEPs recorded from the resting muscle immediately after each exercise set was 218% of the mean preexercise MEP amplitude in normal subjects and 132% in cerebellar patients, indicating postexercise MEP facilitation in both groups. However, postexercise MEP facilitation, compared with the mean preexercise MEP amplitude, was not significant in the patients but was significant in the normal subjects. The amplitudes of MEPs recorded within the first few minutes after fatigue were 44% of the mean preexercise MEP amplitudes in both groups. We conclude that in patients with cerebellar degeneration, postexercise MEP facilitation is significantly reduced, whereas postexercise MEP depression after fatigue is similar to that of normal subjects.

Decreased postexercise facilitation of motor evoked potentials in patients with cerebellar degeneration

Physiology of psychogenic movement disorders

Alcohol challenge and the sensitivity to change of the essential tremor rating assessment scale (TETRAS)

Movement-related cerebellar activation may be due to sensory or motor processing. Ordinarily, sensory and motor processing are obligatorily linked, but in patients who have severe pansensory neuropathies with normal muscle strength, motor activity occurs in isolation. In the present study, positron emission tomography and functional magnetic resonance imaging in such patients showed no cerebellar activation with passive movement, whereas there was prominent movement-related cerebellar activation despite absence of proprioceptive or visual input. The results indicate that motor processing occurs within the cerebellum and do not support the recently advanced view that the cerebellum is primarily a sensory organ.

Movement-Related Cerebellar Activation in the Absence of Sensory Input

Although the role of each part of the brain in voluntary movement is incompletely known, it does appear that the main executor of voluntary movement is the primary motor cortex. Primary motor cortex has monosynaptic and oligosynaptic projections onto spinal motoneurons and a large percentage of cells that are active just prior to movement. Stimulation of these cells produces movement, and averaging of either cellular activity or regional brain potentials from this area shows a clear relationship to muscle activation. Until recently, the predominant view was that the anatomical and physiological relationship between the primary motor cortex and the spinal cord was immutable. Now there are a number of lines of evidence suggesting that the relationship between the motor cortex and its target muscles is modifiable, even in the adult brain. The evidence comes from both animal studies and human studies. This chapter will emphasize the human work and, specifically, information learned using the techniques of transcranial magnetic stimulation (TMS) (Cohen et al. 1991b). With TMS a pulsed magnetic field is applied over the scalp, and the resultant electric current flow in the underlying brain activates neurons. When the neurons activated are in the primary motor cortex, a muscle response or motor evoked potential (MEP) will be produced. By observing the MEPs and varying the stimulus intensity, it is possible to assess excitability of the motor system. Using a figure-8-shaped coil, the stimulus is rather focal, and by systematically moving the coil brain regions can be mapped. Some results will be reviewed using positron emission tomography (PET) with methods for measurement of blood flow. Activity of neurons induces an increase in regional cerebral blood flow, and this effect can be imaged.

Mark Hallett

Papers

Decreased postexercise facilitation of motor evoked potentials in patients with cerebellar degeneration

Physiology of psychogenic movement disorders

Alcohol challenge and the sensitivity to change of the essential tremor rating assessment scale (TETRAS)

Movement-Related Cerebellar Activation in the Absence of Sensory Input

Plasticity of the Human Motor Cortex