Functional Magnetic Resonance Imaging of Visual Object Construction and Shape Discrimination: Relations among Task, Hemispheric Lateralization, and Gender
permalinkJournal of Cognitive Neuroscience - 2001-01-01Georgopoulos AP, Whang K, Georgopoulos MA, Tagaris GA, Amirikian B, Richter W, Kim SG, Ugurbil K10.1162/089892901564180We studied the brain activation patterns in two visual image processing tasks requiring judgements on object construction (FIT task) or object sameness (SAME task). Eight right-handed healthy human subjects (four women and four men) performed the two tasks in a randomized block design while 5-mm, multislice functional images of the whole brain were acquired using a 4-tesla system using blood oxygenation dependent (BOLD) activation. Pairs of objects were picked randomly from a set of 25 oriented fragments of a square and presented to the subjects approximately every 5 sec. In the FIT task, subjects had to indicate, by pushing one of two buttons, whether the two fragments could match to form a perfect square, whereas in the SAME task they had to decide whether they were the same or not. In a control task, preceding and following each of the two tasks above, a single square was presented at the same...
One motor cortex, two different views
Mental Maze Solving
permalinkJournal of Cognitive Neuroscience - 2000-09-01Crowe D, Averbeck B, Chafee M, Anderson JH, Georgopoulos AP10.1162/089892900562426We 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...
Cognition: Mental Rotation
Neural aspects of cognitive motor control
Sleep in a community sample of elderly war veterans with and without Posttraumatic Stress Disorder
permalinkBiological Psychiatry - 2000-03-15Engdahl B, Eberly RE, Hurwitz TD, Mahowald MW, Blake J10.1016/S0006-3223(99)00201-2Background: Although sleep disturbances are commonly reported by individuals with
Posttraumatic Stress Disorder, 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
PTSDsubjects 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
PTSDcompleted 3 nights of polysomnography. Of these participants, 30 met criteria for current
PTSD; three were receiving supportive outpatient psychotherapy.Results: Two statistically significant differences were observed: Those with
PTSDhad 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
PTSDwere lower than the perceptions of non-
PTSDparticipants. Although participants with untreated obstructive sleep apnea and sleep movement disorders were not included in the...
Motor Area Activity During Mental Rotation Studied by Time-Resolved Single-Trial Functional Magnetic Resonance Imaging
permalinkJournal of Cognitive Neuroscience - 2000-03-01Richter W, Somorjai R, Summers R, Jarmasz M, Menon RS, Gati JS, Georgopoulos AP, Tegeler C, Ugurbil K, Kim SG10.1162/089892900562129The 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
Functional Magnetic Resonance Imaging. 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...
Inactivation of parietal and prefrontal cortex reveals interdependence of neural activity during memory-guided saccades
Varied duration of congenital hypothyroidism potentiates perseveration in a response alternation discrimination task
permalinkNeuroscience Research - 2000-02-01MacNabb C, O'Hare E, Cleary J, Georgopoulos AP10.1016/S0168-0102(99)00111-XThe 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...
Trauma exposure, resilience, social support, and Posttraumatic Stress Disorder construct validity among former prisoners of war
permalinkSocial Psychiatry and Psychiatric Epidemiology - 2000-02-01Gold PB, Engdahl B, Eberly RE, Blake RJ, Page WF, Frueh BC10.1007/s001270050006Background: The aim of this study was to investigate predictors of persistent symptoms of
PTSDand to examine the construct validity of
PTSDin 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
PTSDsymptomatology 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
PTSDmodule of the Structured Clinical Interview for DSM (SCID). Results: The CMI provided only partial coverage of
PTSDcriteria 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
PTSDsymptoms into criterion groups, although there was not a perfect...
Directional tuning profiles of motor cortical cells
permalinkNeuroscience Research - 2000-01-01Amirikian B, Georgopoulos AP10.1016/S0168-0102(99)00112-1The 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...
Congenital hypothyroidism impairs response alternation discrimination behavior
permalinkBrain Research - 1999-11-20MacNabb C, O'Hare E, Cleary J, Georgopoulos AP10.1016/S0006-8993(99)02038-7The 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...
Neural Coding of Finger and Wrist Movements
permalinkJournal of Computational Neuroscience - 1999-05-01Georgopoulos AP, Pellizzer G, Poliakov AV, Schieber MH10.1023/A:1008810007672Previous 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...
News in Motor Cortical Physiology
Motor Cortical Encoding of Serial Order in a Context-Recall Task
Multidimensional scaling analyses of two construction-related tasks
permalinkExperimental Brain Research - 1999-03-01Whang K, Crowe D, Georgopoulos AP10.1007/s002210050678Representations 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...
Drawing under visuomotor incongruence
permalinkExperimental Brain Research - 1999-03-01Pellizzer G, Richter W, Georgopoulos AP10.1007/s002210050666Six 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...
Cortical Populations and Behaviour: Hebb's Thread
Selection and Initiation of Motor Patterns
Neural Networks and Modeling of Neuronal Networks