The experiments Feldman and Levin suggest do not definitively test their proposed solution to the problem of selecting muscle activations. Their test of the movement directions that elicit EMG activity can be interpreted without regard to the form of the central commands, and their fast elbow flexion test is based on a forward computation that obscures the insensitivity of the predicted trajectory to the details of the putative commands.

We provide a brief overview of the shift toward the intrinsic view of brain activity, describing in particular the structural and functional connectivity patterns of the “Default mode network”. We then consider the Default mode network in a specifically cognitive setting and ask what changes the focus on the Default mode network and other sorts of intrinsic activity require from models put forward by cognitive neuroscientists.

We argue that the concept of a control variable (CV) as described by Feldman and Levin needs to be revised because it does not account for the influence of sensory feedback from the periphery. We provide evidence from the realm of rhythmic movements that sensory feedback can permanently alter the frequency and phase of a centrally generated rhythm.

The authors ofImages of mindhave been highly successful in unravelling the neural basis of complex brain functions. Their emphasis on top-down processingin experimental neuroscience is especially important and, it is hoped, influential. Tracking brain activation accurately botli in space and in time would benefit from studiesofindividual subjects without relying on grand average data.

The lambda model predicts that the command received by each motor nucleus during locomotion is specific for the joint at which its muscle acts and is independent of external conditions. However, investigation of the commands received by motor nuclei during fictive locomotion and of the sensitivity of these commands to feedback from the limb during locomotion indicates that neither condition is satisfied.

Nach einer kurzen Übersicht überDescartes' mechanistiche Theorie der somatischen Funktionen und der Reproduktion, wird in der vorliegenden Arbeit die Entwicklung dieser Theorie bis zur neuesten Zeit beschrieben. Sodann wird eine Übersicht gegeben über die vitalistische Theorie, welche unter wissenschaftlichen Forschern bis zur Mitte des vorigen Jahrhunderts vorherrschte. Dann werden die Gründe dafür angegeben, dass diese Theorie des Vitalismus ungefähr um diese Zeit verlassen wurde, um durch die mechanistische Theorie ersetzt zu werden. Diese ihrerseits ist jedoch auf einer unbegründeten metaphysischen Auffassung (...) vom Wesen der Wirklichkeit aufgebaut. Nehmen wir sie an, so können wir die synthetischen Einheit, die Gesamterscheinungsreihe, die wir unter dem Namen Reproduktion und Körperfunktion zusammenfassen, nicht richtig beschreiben. Der Begriff „Leben” ist eine Synthese aller Beziehungen, die zwischen dem Organismus und seiner Umwelt bestehen. Diese Auffassung des Lebens ist die Grundlage der Biologie, daher ist denn auch Biologie eine selbständige, unabhängige Wissenschaft.Zuletzt wird der Reflexbegriff behandelt. Die mechanistische Auffassung des Reflexbegriffes ist unrichtig, da alle Reflexfunktion synthetischen, oder integrativen Charakter hat. Wäre dem nicht so, dann würde das Nervensystem lediglich Chaos hervorzubringen imstande sein. Biologie, ohne die Gegebenheit des Lebens vorauszusetzen, ist unmöglich und wissenschaftliches Voraussagen auf dem Gebiete der Biologie ist überall nur auf Grund dieser Voraussetzung möglich.Après avoir donné un bref aperçu de la théorie mécanique cartésienne de l'activité corporelle et de la reproduction, l'article contenu dans cette revue trace le développment de cette théorie jusqu'à notre temps. Un bref aperçu est donné ensuite de la théorie vitaliste qui prévalait parmi les observateurs scientifiques jusqu'au milieu du siècle dernier. Après cela sont exposées les raisons pour lesquelles la théorie du vitalisme fut abandonnée de nos jours et il est démontré, qu'il est généralement admis que l'abandon de cette théorie implique l'adoption de la conception mécanique. Cette conception, cependant, est basée sur une conception métaphysique mal fondée se rapportant à la nature de la réalité et, en l'acceptant, nous ne pouvons exprimer ou décrire l'intégration qui apparait dans les phénomènes de reproduction et d'activité corporelle de toutes sortes. La vie c'est l'intégration soutenue s'étendant sur toutes les relations entre l'organisme et son entourage; et la conception de la vie, c'est la base de la biologie, de sorte que la biologie est une science indépendant.l'Article termine par une discussion de l'action-réflexe et démontre qu'une interprétation mécanique de l'action-réflexe est inadéquate, puisque l'intégration est incluse dans toute action-réflexe; car si tel n'était pas le cas, le système nerveux ne serait autre chose qu'un mécanisme à produire du chaos. La biologie ne peut pas se passer de la vie, comme sa conception fondamentale, et les prédicitions en matière de biologie sont toujours basées sur cette conception. (shrink)

PET detects changes in metabolism between task periods and is thus insensitive to areas that are activated during all or most of cognition. Depth-recorded, evokedpotentials indicate that many multimodal and limbic cortical areas may be activated during most cognitive tasks. Thus, PET may be insensitive to some core processes of awareness that are difficult to eliminate from the control periods.

Extrapersonal frames of reference for aimed movements are representationally convenient. They may, however, carry associated costs when the movement is executed in terms of the complex coordination of multiple joints they require. Studies that have measured both fingertip and joint paths suggest the motor systems may seek a compromise between simplicity of extrapersonal spatial representation and computational simplicity of multi-joint execution.

On the basis of neuroiinaging studies, Posner & Raichle summarily report that the prefrontal cortex is involved in executive functioning and attention. In contrast to that superficial view, we briefly describe a testable model of the kinds of representations that are stored in prefrontal cortex, which, when activated, are expressed via plans, actions, thematic knowledge, and schemas.

Models of central control variables (CVs) that are expressed in positional reference frames and rely on proprioception as the dominant specifier of muscle activation patterns have not yet been shown to be adequate for the description of fast, voluntary movement, even of single joints. An alternative model with illustrative data is proposed.

Kinematic properties of reaching movements reflect constraints imposed on the joint angles. Contemporary models present solutions to the redundancy problem by a pseudoinverse procedure (Whitney 1969) or without any inversion (Berkenblit et al. 1986). Feldman & Levin suggest a procedure based on a regular inversion. These procedures are considered as an outcome of a more general approach.

Research reported by Posner & Raichle may be usefully applied to the rehabilitation of persons with brain damage. Their findings are related to the “dual premotorsystems hypothesis” that reciprocally interactive medial and lateral brain systems are involved in attention and learning. Recent studies show that “brain healing” occurs through dynamic reorganization involving attentional networks postulated by Posner & Raichle.

The following statement from James’ 1884 essay in Mind is repeated in his later work and appears often in secondary sources as a summary of his celebrated theory of the emotions:Our natural way of thinking about these standard emotions is that the mental perception of some fact excites the mental affection called the emotion, and that this latter state of mind gives rise to the bodily expression. My thesis on the contrary is that the bodily changes follow directly the Perception (...) of the exciting fact, and that our feeling of the same changes as they occur IS the emotion. Common sense says, we lose our fortune, are sorry, and weep; we meet a bear, are frightened and run; we are insulted by a rival, are angry and strike. The hypothesis here to be defended says that this order of sequence is incorrect, that the one mental state is not immediately induced by the other, that the bodily manifestation must first be interposed between, and that the more rational statement is that we feel sorry because we cry, angry because we strike, afraid because we tremble, and not that we cry, strike, or tremble because we are sorry, angry, or fearful as the case may be. Without the bodily states following on the perception the latter would be purely cognitive in form, pale, colorless, destitute of emotional warmth. We might then see the bear and judge it best to run, receive the insult and deem it right to strike, but we would not actually feel afraid or angry. (shrink)

Images of mindis an exciting book, well-written and wellorganized, but many of the connections the authors draw between PET scan results and more general psychological issues are somewhat strained.

The search for simplifying principles in motor control motivates the target article. One method that the CNS uses to simplify the task of controlling a limb's mechanical properties is absent from the article. Evidence from multi-joint, force-field measurements and from kinematics that points to the existence of multi-joint primitives as control variables is discussed.

Recent results have shown that the relative activation of muscles is different for isometric contractions and for movements. These results exclude an explanation of muscle activation patterns by a combination ofreciprocal and coactivation commands. These results also indicate that joint stiffness is not uniquely determined and that it may be different for isometric contractions and movements.

We argue that the function of the cerebellum is more than just an error-detecting mechanism. Rather, the cerebellum plays an important role in all movements. The bias in (re)calibration is an unfortunate restrictive result of a very successful and important experiment, [SMITH, THACH].