One motor cortex, two different views

To the editorHere we refute claims by Todorov1 and Scott7 that the importance of target direction as an explanatory factor for cortical activity in a regression analysis we performed5 is an 'artifact' of a square-root transformation of neural discharge rates. Specifically, it was touted by Scott7 that "squaring [sic] the discharge rate of neurons in order to stabilize the variance … causes a dramatic increase in the percentage of neurons that appear to represent movement direction (from 17% [sic] to 43% in Todorov's model)."

Mental Maze Solving

We sought to determine how a visual maze is mentally solved. Human subjects (N = 13) viewed mazes with orthogonal, unbranched paths; each subject solved 200-600 mazes in any specific experiment below. There were four to six openings at the perimeter of the maze, of which four were labeled: one was the entry point and the remainder were potential exits marked by Arabic numerals. Starting at the entry point, in some mazes the path exited, whereas in others it terminated within the maze. Subjects were required to type the number corresponding to the true exit (if the path exited) or type zero (if the path did not exit). In all cases, the only required hand movement was a key press, and thus the hand never physically traveled through the maze. Response times (RT) were recorded and analyzed using a multiple linear regression model. RT increased as a function of key parameters...
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Cognition: Mental Rotation

Cognitive neuroscience seeks to identify brain events underlying cognitive operations. Scientists already know that the activity of single cells in specific areas of the cerebral cortex changes during the performance of particular tasks, presumably in association with the task. The figures above represent neuronal vector firing changes in the motor cortex of a monkey that are associated with the cognitive operation of mental rotation (moving a handle in a direction at an angle to the stimulus). The direction of a movement in space can be represented in the motor cortex as a "neuronal population vector"; a population vector is the weighted vector sum of contributions of directionally tuned neurons. In the example represented above, a monkey was trained to move a freely movable handle either toward a light stimulus (left panel) or at a 90° angle away from the stimulus (middle panel). Individual recordings from neurons in the motor cortex are...
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Neural aspects of cognitive motor control

Traditionally, motor and cognitive functions were studied separately; however, the investigation of processes at the interface between cognition and action has become more and more popular recently. Typical research goals include the identification of the processes involved using experimental psychological methods, and understanding the neural mechanisms underlying these processes using neurophysiological and functional neuroimaging methods. Specifically, there has been a special emphasis during the past few years on timing mechanisms, practice effects, and the application of rules in guiding action. New information concerning the neural mechanisms involved is being acquired at a rapid pace, albeit mostly within a descriptive framework. With respect to specific brain areas, a key finding has been the clear involvement of the primary motor cortex in complex tasks engaging diverse motor and cognitive dimensions.

Sleep in a community sample of elderly war veterans with and without

Posttraumatic Stress Disorder

Posttraumatic Stress Disorder (PTSD)

A complex psychiatric syndrome that develops in response to trauma exposure. Individuals with PTSD experience intrusive recollections or reexperiencing of the traumatic event, avoidance of trauma reminders, emotional numbing, and hyperarousal. In addition, PTSD is associated with high rates of concomitant physical and mental health problems, increased health care use, and impairment in social and occupational functioning. Almost 7% of the general population and up to 30% of veterans meet lifetime criteria for PTSD. Indeed, PTSD is one of the most common psychiatric disorders, representing a significant and costly public health concern.

Background: Although sleep disturbances are commonly reported by individuals with , objective findings have been inconsistent, due in part to small sample sizes, comorbid psychiatric disorders, variations in the recentness of trauma exposure, and the use of subjects involved in psychiatric treatment.Methods: A community sample of elderly males (n = 59) exposed to war trauma 28-50 years ago and free from sleep-affecting medications and disorders other than completed 3 nights of polysomnography. Of these participants, 30 met criteria for current ; three were receiving supportive outpatient psychotherapy.Results: Two statistically significant differences were observed: Those with had a higher percentage of rapid eye movement (REM) sleep and fewer arousals from non-REM sleep. The perceptions of sleep quality among the participants with were lower than the perceptions of non- participants. Although participants with untreated obstructive sleep apnea and sleep movement disorders were not included in the...
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Motor Area Activity During Mental Rotation Studied by Time-Resolved Single-Trial

Functional Magnetic Resonance Imaging

Functional Magnetic Resonance Imaging (fMRI)

A functional neuroimaging procedure using MRI technology that measures brain activity by detecting changes associated with blood flow. This technique relies on the fact that cerebral blood flow and neuronal activation are coupled. When an area of the brain is in use, blood flow to that region also increases.[citation needed] The primary form of fMRI uses the blood-oxygen-level dependent (BOLD) contrast, discovered by Seiji Ogawa. This is a type of specialized brain and body scan used to map neural activity in the brain or spinal cord of humans or other animals by imaging the change in blood flow (hemodynamic response) related to energy use by brain cells. Since the early 1990s, fMRI has come to dominate brain mapping research because it does not require people to undergo shots, surgery, or to ingest substances, or be exposed to ionising radiation, etc.

The functional equivalence of overt movements and dynamic imagery is of fundamental importance in neuroscience. Here, we investigated the participation of the neocortical motor areas in a classic task of dynamic imagery, Shepard and Metzler's mental rotation task, by time-resolved single-trial . The subjects performed the mental-rotation task 16 times, each time with different object pairs. Functional images were acquired for each pair separately, and the onset times and widths of the activation peaks in each area of interest were compared to the response times. We found a bilateral involvement of the superior parietal lobule, lateral premotor area, and supplementary motor area in all subjects; we found, furthermore, that those areas likely participate in the very act of mental rotation. We also found an activation in the left primary motor cortex, which seemed to be associated with the right-hand button press at the end of the task...
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Inactivation of parietal and prefrontal cortex reveals interdependence of neural activity during memory-guided saccades

Dorsolateral prefrontal and posterior parietal cortex share reciprocal projections. They also share nearly identical patterns of neuronal activation during performance of memory-guided saccades. To test the hypothesis that the reciprocal projections between parietal and prefrontal neurons may entrain their parallel activation, the present experiments have combined cortical cooling in one cortical area with single-unit recording in the other to more precisely determine the physiological interactions between the two during working memory performance. The activity of 105 cortical neurons during the performance of an oculomotor delayed response (ODR) task (43 parietal neurons during prefrontal cooling, 62 prefrontal neurons during parietal cooling) was compared across two blocks of trials collected while the distant cortical area either was maintained at normal body temperature or cooled. The mean firing rates of 71% of the prefrontal neurons during ODR performance changed significantly when parietal cortex was cooled. Prefrontal neurons the activity of which was modulated during...
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Varied duration of congenital hypothyroidism potentiates perseveration in a response alternation discrimination task

The behavior of five groups of rats (seven rats per group) made hypothyroid for varying lengths of time and one group of seven normal control rats was assessed under forced alternation fixed-ratio (FR1, FR3, FR5 and FR10), alternating lever cyclic-ratio (ALCR) and progressive-ratio (PR3) schedules of reinforcement. Hypothyroidism was produced by adding methimazole (MMI) to the drinking water of pregnant dams from embryonic day E16 to postnatal day P25. Four groups were given replacement thyroxine (T4) injections beginning at specific time points (P1, P7, P13, and P19). There were no differences in behavioral performance between control and experimental groups under the FR schedule, which indicates that the animals' sensorimotor abilities were intact. Under the forced ALCR schedule, all groups reached criteria similarly. However, under the choice lever ALCR schedule, control animals and those which received T4 replacement from early on (P1, P7, P13 groups) performed well and all had reached criteria...
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Trauma exposure, resilience, social support, and

Posttraumatic Stress Disorder

Posttraumatic Stress Disorder (PTSD)

A complex psychiatric syndrome that develops in response to trauma exposure. Individuals with PTSD experience intrusive recollections or reexperiencing of the traumatic event, avoidance of trauma reminders, emotional numbing, and hyperarousal. In addition, PTSD is associated with high rates of concomitant physical and mental health problems, increased health care use, and impairment in social and occupational functioning. Almost 7% of the general population and up to 30% of veterans meet lifetime criteria for PTSD. Indeed, PTSD is one of the most common psychiatric disorders, representing a significant and costly public health concern.

construct validity among former prisoners of war

Background: The aim of this study was to investigate predictors of persistent symptoms of and to examine the construct validity of in a national sample of 270 World War II and Korean Conflict prisoners of war (POWs). Method: POWs were interviewed at two points in time (1965 and 1990). Predictors included symptomatology measured in 1965 by items from the Cornell Medical Index (CMI), severity of captivity trauma, resilience factors, and post-trauma social support. The criterion, symptomatology in the early 1990s, was evaluated with the module of the Structured Clinical Interview for DSM (SCID). Results: The CMI provided only partial coverage of criteria and appeared to provide only a general index of distress. Clustering of SCID items in two-dimensional space via multidimensional scaling analysis offers some construct validation for the DSM's differentiation of symptoms into criterion groups, although there was not a perfect...
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Directional tuning profiles of motor cortical cells

The directional tuning profiles of motor cortical cells are commonly described by a cosine tuning function with three adjustable parameters (Georgopoulos, A.P., Kalaska, J.F., Crutcher, M.D., Caminiti, R., Massey, J.T., 1982. On the relations between the direction of two-dimensional (2D) arm movements and cell discharge in primate motor cortex. J. Neurosci. 2, 1527-1537). In this study the variation in the shape of the directional tuning profiles among a population of cells recorded from the arm area of the motor cortex of monkeys using movements in 20 directions, every 18°, was examined systematically. This allowed the investigation of tuning functions with extra parameters to capture additional features of the tuning curve (i.e. tuning breadth, symmetry, and modality) and determine an 'optimal' tuning function. These functions provided better fit than the standard cosine one. The optimal function for the large majority of tuned cells was unimodal (84%), and only for a few of...
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Congenital hypothyroidism impairs response alternation discrimination behavior

The behavior of six congenitally hypothyroid and six normal control rats was assessed under forced alternation fixed-ratio, alternating lever cyclic-ratio (ALCR) and progressive-ratio schedules of reinforcement. Hypothyroidism was produced by adding methimazole (MMI) to the drinking water of pregnant dams from embryonic day 16 to postnatal day 25. There were no differences in behavioral performance between MMI-treated and control animals under the fixed-ratio and progressive ratio schedules. There were also no differences in circulating triiodothyronine levels between groups at the end of the study. Under the ALCR schedule, when alternation of responding was forced during the first three cycles but both levers (choice) were presented during the last three cycles (correct lever active), the entire control group reached a competency criteria in nine sessions. In contrast, only two MMI-treated animals reached criteria after 17 sessions, and the remaining four MMI-treated animals did not reach criteria by 30 sessions of training. These...
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Neural Coding of Finger and Wrist Movements

Previous work (Schieber and Hibbard, 1993) has shown that single motor cortical neurons do not discharge specifically for a particular flexion-extension finger movement but instead are active with movements of different fingers. In addition, neuronal populations active with movements of different fingers overlap extensively in their spatial locations in the motor cortex. These data suggested that control of any finger movement utilizes a distributed population of neurons. In this study we applied the neuronal population vector analysis (Georgopoulos et al., 1983) to these same data to determine (1) whether single cells are tuned in an abstract, three-dimensional (3D) instructed finger and wrist movement space with hand-like geometry and (2) whether the neuronal population encodes specific finger movements. We found that the activity of 132/176 (75%) motor cortical neurons related to finger movements was indeed tuned in this space. Moreover, the population vector computed in this space predicted well the instructed finger...
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News in Motor Cortical Physiology

Motor cortical activity relates to static motor parameters (isometric force, limb position) under static conditions but predominantly to dynamic parameters (change of force, limb velocity) under dynamic conditions. This dual relation conceptually unifies the role of motor cortex in the control of isometric force and movement.

Motor Cortical Encoding of Serial Order in a Context-Recall Task

The neural encoding of serial order was studied in the motor cortex of monkeys performing a context-recall memory scanning task. Up to five visual stimuli were presented successively on a circle (list presentation phase), and then one of them (test stimulus) changed color; the monkeys had to make a single motor response toward the stimulus that immediately followed the test stimulus in the list. Correct performance in this task depends on memorization of the serial order of the stimuli during their presentation. It was found that changes in neural activity during the list presentation phase reflected the serial order of the stimuli; the effect on cell activity of the serial order of stimuli during their presentation was at least as strong as the effect of motor direction on cell activity during the execution of the motor response. This establishes the serial order of stimuli in a motor task as an important...
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Multidimensional scaling analyses of two construction-related tasks

Representations involved in two construction-related tasks were analyzed by multidimensional scaling (MDS), a statistical technique that allows the dimensions of internal representations to be derived from empirically obtained judgment data. The tasks involved judgments of how similar two objects were and how well they fitted together; these judgments are related to copying and assembly abilities that are impaired in constructional apraxia. Analyses of numerical subjective ratings and response times for these judgments showed that within the same set of geometric objects, different shape-related properties were emphasized under different task conditions. The similarity judgment depended most on a representational dimension related to enclosure of space, while the fit judgment depended to a greater extent on a dimension related to the objects' symmetry properties. This pattern of results was found in both subjective ratings and response times, as analyzed by MDS and by confirmatory classical statistics. The findings suggest that construction-related tasks depend...
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Drawing under visuomotor incongruence

Six human subjects were asked to draw ellipses presented on a screen by moving a manipulandum that controlled the position of a cursor. Six visual templates were used, which comprised three different ellipses displayed either horizontally or vertically; the ratio between the major and minor axes was 2, 4, or 5. For each visual template, the gains were set such that the movement trajectories required to trace the template with the cursor corresponded to one of six ellipses. Thus these movement ellipses were horizontal or vertical with a ratio between major and minor axes of 2, 4, or 5. All 36 combinations of six visual ellipses and six required movement ellipses were used. Therefore, in some conditions the required movement ellipse had a different orientation (with respect to the major axis) than the visual template. These conditions were called orientation incongruent, whereas, when the orientation of the required movement ellipse matched...
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Cortical Populations and Behaviour: Hebb's Thread

This paper discusses work on the function of the motor cortex as revealed by single cell recordings in monkeys and artificial neural network modelling. Our key conceptual approach both in behavioural neuroscience and neural network modeling of motor cortical function relies on reconstructing, visualizing, and modelling the activity in neuronal populations, indeed a key concept advanced by Hebb (1949). The behaviour investigated ranges from exertion of isometric force to pointing movements to complex cognitive processing. The functional properties of single cells with respect to the direction of movement in space are described as well as a population code which provides a unique measure for this direction. Finally, the results of modeling studies are discussed in which directional population activity is used as an input to an artificial neural network to drive a simulated arm.

Selection and Initiation of Motor Patterns

Successful locomotion in vertebrates requires not only generation of the appropriate propulsive synergy (flying, swimming, or walking), but also goal-directed steering and control of body orientation. In most vertebrates, a correct positioning of each foot is also required during selected phases of the movement. This review focuses on the role of the forebrain and brainstem control in the initiation of locomotion. It considers the basal ganglia, hypothalamus, the mesencephalic locomotor region, including the cuneiform and pedunculoponltine regions, as well as the medullary reticular areas. The various corticospinal systems are also reviewed because they most likely contribute to accurate foot placement during locomotion over a complex terrain.

Neural Networks and Modeling of Neuronal Networks

The past decades have seen an explosive growth in accumulation of experimental data in neuroscience research. The detailed anatomical and physiological data alone, however, are not enough to understand how the nervous system works. It is the recognition of this fact that makes modeling studies a significant part of mainstream research in neuroscience. The combination of theoretical methods, including mathematical analyses and computer simulations, together with modern experimental techniques has led to the emergence of a new discipline of computational neuroscience with the ultimate goal of explaining how neural signals represent and process information in the brain. Modeling of neuronal networks is a powerful tool that enables accomplishment of this goal by understanding how specific parts of the nervous system perform certain operations (for instance, learning specific motor skills, computing the direction of reaching movement, decoding spatial information, etc.) and is complementary to traditional techniques in neuroscience research.

Neural Mechanisms of Motor Cognitive Processes: Functional MRI and Neurophysiological Studies

The neural mechanisms of cognitive processes cannot be elucidated using a single method; instead, useful insight can be gained by employing various approaches. In this chapter, the author attempts a discussion in this direction, namely the investigation of the mechanisms underlying some motor cognitive processes using behavioral, neurophysiological, and function neuroimaging methods.