Hemispheric control of unilateral and bilateral movements of proximal and distal parts of the arm as inferred from simple reaction time to lateralized light stimuli in man

Summary In 12 normal, right-handed male subjects simple reaction time of key-pressing and leverpulling responses to light flashes presented in the right or left visual fields was faster with the arm ipsilateral to the visual stimulus, provided the responses were made unilaterally. Key-pressing responses involved a movement of a single finger, whereas lever-pulling responses involved an integrated movement of the proximal parts of the arm. The mean difference in reaction time between reactions ipsilateral to the stimulus and reactions contralateral to the stimulus was about 2 ms for both key-pressing and lever-pulling responses. When key-pressing and lever-pulling responses to a single lateralized light stimulus were made bilaterally, the advantage in favor of the ipsilateral responses was still present, although it was mainly limited to the right hand, on key-pressing, whereas it was completely absent on lever pulling.The difference between ipsilateral and contralateral reactions on unilateral responding, whether proximal or distal, is attributed to the consistent initiation of the response by the contralateral hemisphere. Given that a lateralized visual stimulus is projected to the opposite hemisphere, ipsilateral responses can be integrated within a single hemisphere, whereas contralateral responses are integrated interhemispherically and therefore require additional time. The reduction or lack of the ipsilateral advantage on bilateral responding is attributed to the engagement of a bilaterally distributed motor control that is preferentially directed to the proximal musculature.     

The effect of response execution on P3 latency, reaction time, and movement time.

This study examined the effect of response selection and execution on P3 latency during the performance of simple reaction time (RT) and stimulus-response compatibility tasks. Response time on these tasks was defined in terms of RT and movement time (MT). Event-related brain potentials were recorded from 67 female participants concurrently with the performance measures. On the simple RT task, the distance of the response button from the home button was varied (7, 15, and 23 cm). When stimulus evaluation demands were minimal, response execution affected P3 latency, with increased response button distance resulting in increased P3 latency. However, these movement effects were modest, and in most protocols, would not be a confounding factor. The stimulus-response compatibility task examined the interaction of stimulus evaluation demands and response requirements. RT, MT, and P3 latency were affected by stimulus congruency, whereas RT and P3 amplitude were affected by response compatibility.     

Simple and choice reaction time in dementia: Clinical implications

The present study investigated differences between normal elderly subjects matched for age and education and patients with dementia of the Alzheimer's type (DAT) on two measures of reaction time (RT). Statistically significant group differences clearly demonstrate that normal elderly subjects have faster RT than subjects with senile dementia on all RT tasks. The DAT patients were most clearly differentiated in terms of overall group means and clinical classification from their age-matched counterparts on the choice RT task. Eleven of 12 (92%) DAT patients displayed choice RT's 2 or more standard deviations above those of age-matched normals. While both RT measures were discriminative between patients and normals, the overall results argue for increased sensitivity when choice is required in RT in accessing the cognitive deficits in DAT.     

Role of the cerebellum in visuomotor coordination

The initiation of coupled eye and arm movements was studied in six patients with mild cerebellar dysfunction and in six age-matched control subjects. The experimental paradigm consisted of 40 deg step-tracking elbow movements made under different feedback conditions. During tracking with the eyes only, saccadic latencies in patients were within normal limits. When patients were required to make coordinated eye and arm movements, however, eye movement onset was significantly delayed. In addition, removal of visual information about arm versus target position had a pronounced differential effect on movement latencies. When the target was extinguished for 3 s immediately following a step change in target position, both eye and arm onset times were further prolonged compared to movements made to continuously visible targets. When visual information concerning arm position was removed, onset times were reduced. Eye and arm latencies in control subjects were unaffected by changes in visual feedback. The results of this study clearly demonstrate that, in contrast to earlier reports of normal saccadic latencies associated with cerebellar dysfunction, initiation of both eye and arm movements is prolonged during coordinated visuomotor tracking thus supporting a coordinative role for the cerebellum during oculo-manual tracking tasks.     

Motor cortex excitability changes during imagery of simple reaction time

Imagining motor actions is enough to enhance cortical motor excitability. However, the fact that execution of the motor task has to be inhibited should have a correlate on the extent of cortical excitability enhancement. Therefore, we examined the possible differences between real and motor imagery of simple reaction time tasks (SRT) in the facilitation of the motor-evoked potential (MEP) to transcranial magnetic stimulation (TMS) and in the reduction of short-interval intracortical inhibition (SICI) taking place before the movement onset. Thirteen healthy volunteers were requested to perform visual real or imaginary SRT tasks (rSRT and iSRT) with their dominant hand. For rSRT, subjects had to perform a rapid isometric squeeze as soon as possible after the imperative signal. For iSRT they had to imagine the same movement without actually doing it. Electromyographic (EMG) signals were recorded from the first dorsal interosseus (FDI) muscle. The mean EMG onset was calculated for each subject in rSRT trials. Single-and paired-pulse TMS (at an interstimulus interval of 2.5 ms) were applied at rest and at time intervals of −25, −50, −75, −100 and −125 ms before the expected real (rSRT) mean EMG onset. In rSRT there was a significant increase of MEP to single-pulseTMS at the intervals of −50 and −25 ms, and in iSRT at −50 ms in comparison to the rest condition. % SICI changes were significantly reduced at the intervals of −75, −50 and −25 ms, before EMG the onset in rSRT and at −50 and −25 in iSRT (P < 0.05) in comparison to % SICI changes at rest. The differences between MEPs to spTMS and MEP to ppTMS were significantly larger at rest, −125 and −100 ms intervals in rSRT, and at all intervals in iSRT. Imagining to move causes an increase in corticospinal excitability and a decrease in intracortical inhibition that follow a temporal profile similar to those observed with real movements. However, complete removal of SICI happened only in rSRT at the shortest intervals before the EMG onset. Such action may delineate new tool in motor rehabilitation of patients who have limitation to move.     

Physical exercise facilitates motor processes in simple reaction time performance: an electromyographic analysis

The aim of the current study was to assess the effects of physical exercise on simple reaction time performance. Participants performed a simple reaction time task twice, one time during physical exercise and another time without exercise. Electromyographic signals were recorded from the thumb of the responding hand to fraction reaction time in pre-motor and motor time. The results showed that exercise shortened motor time but failed to affect pre-motor time. This pattern of findings is consistent with previous studies examining the effects of physical exercise on choice reaction time.     

Effects of reappearance of fixated and attended stimuli upon saccadic reaction time

Summary The effects of visual attention and fixation upon the distribution of saccadic latencies: express (E-), fast regular (FR-), and slow regular (SR-) saccades were investigated. Extinguishing a fixation or an attention point 200–300 ms before target onset increases the incidence of E-saccades while concurrently decreasing the proportion of SR-saccades. Since this extinction forces a disengaging of attention, these changes in relative proportions of saccades reflect the elimination of one of the steps involved in programming saccades. It is shown that a previously attended stimulus has a favored status relative to other stimuli in the visual field. If, after being turned off, the previously attended fixation point or a peripheral attention stimulus is turned on near the time of the target's appearance, the occurrence of the E-saccades is greatly reduced. However, the appearance of any other stimulus in the visual field at or near the time of the target onset does not inhibit E-saccades. Contrary to the conclusions reached by Posner and Cohen (1984), a stimulus presented at the formerly attended location can attract attention more efficiently than a stimulus presented at another, new location.     

Experimental disentangling of spatial-compatibility and interhemispheric-relay effects in simple reaction time (Poffenberger paradigm)

Spatial-compatibility effects can be obtained in simple reaction time (SRT) provided that spatially distinct responses are frequently required. Since this effect is limited to trials with relatively long reaction times (RTs), Hommel (1996b) proposed that if the response does not occur shortly after stimulus detection, then the spatial code of the stimulus can interfere with that of the response. A series of experiments is reported showing that (a) spatial compatibility in SRT to lateralized stimuli is not an alternative, but rather a complementary, explanation to interhemispheric transfer time (contrary to what Hommel surmised), and (b) the spatial compatibility component is essentially limited to the first trial after shifting response preparation from one-half of the visual fields to the other, suggesting a mechanism akin to an orienting response.This research was made possible by bursaries from the National Science and Engineering Research Council (NSERC) of Canada and the Fonds pour la Formation des Chercheurs et dAide à la Recherche (FCAR) of Quebec to the second author, and NSERC, FCAR and Fonds de Recherche en Santé (Quebec) grants to the first and third authors     

Shortening of simple reaction time by peripheral electrical and submotor-threshold magnetic cortical stimulation

 Subthreshold transcranial magnetic stimulation (TMS) over the motor cortex can shorten the simple reaction time in contralateral arm muscles if the cortical shock is given at about the same time as the reaction stimulus. The present experiments were designed to investigate whether this phenomenon is due to a specific facilitatory effect on cortical circuitry. The simple visual reaction time was shortened by 20–50 ms when subthreshold TMS was given over the contralateral motor cortex. Reaction time was reduced to the same level whether the magnetic stimulus was given over the bilateral motor cortices or over other points on the scalp (Cz, Pz). Indeed, similar effects could be seen with conventional electrical stimulation over the neck, or even when the coil was discharged (giving a click sound) near the head. We conclude that much of the effect of TMS on simple reaction time is due to intersensory facilitation, although part of it may be ascribed to a specific effect on the excitability of motor cortex. Received: 15 July 1996 / Accepted: 25 February 1997     

The human brain at stage 16, including the initial evagination of the neurohypophysis

Summary Thirty-nine sectioned embryos of stage 16 were studied. Up to this stage the amygdaloid body is derived entirely from the medial eminence, which was purely diencephalic in stage 14, but now extends also to the telencephalon. The area of the future olfactory bulb is indicated by the presence of olfactory fibres entering the brain wall; the future olfactory tubercle is characterized by cellular islands. The presence of the hippocampal thickening and various histological features make it possible to outline the main, future cortical areas already at this early stage: archi-, paleo-, and neopallium. Hippocampus and area dentata correspond to the areas identified by Hines (1922) and Bartelmez and Dekaban (1962) but not to those identified by Humphrey (1966). The interventricular foramen is wide. The cerebral hemispheres grow rostrally and dorsally, thereby forming the beginning of the longitudinal fissure. Apart from the commissure of the superior colliculi, which began to appear in advanced embryos of stage 14, fibres of the posterior commissure are now present in some specimens. The neurohypophysis is apparent in fewer than half of the embryos. The marginal ridge (zona limitans intrathalamica) separates the dorsal from the ventral thalamus. Cranial nerve 3 emerges from M2. M1 has become shorter. Important pathways are beginning: the olfactory route by the olfactory fibres and the medial forebrain bundle; the vestibular by vestibulocerebellar and vestibulospinal fibres; gustatory by chorda tympani, nervus intermedius, and tractus solitarius. Fibres of the cochlear nerve are noted. The first parasympathetic ganglia, submandibular and ciliary, are identifiable. Asymmetry of the cerebral hemispheres was noted in one specimen.Abbreviations (Figs. 1–13) Aff. Common afferent tract - A.-H. Adenohypophysial pouch - Amyg. Area of the future amygdaloid body - Aq. Aqueduct - Bas. Basilar artery - bm.S. Basal mesencephalic sulcus - Cer. Cerebellum - Ch. Chiasmatic plate - Comm. Commissural plate - X P Posterior commissure - X 4 Commissure of the trochlear nerve - X s.C. Commissure of the superior colliculi - Cr. Terminal-vomeronasal neural crest - D caudalmost rhombomere - De Area dentata - Di. Diencephalon - d.F. dorsal funiculus - d. Th. dorsal thalamus - E Area epithelialis - Ep. Epiphysis - Hab. Habenular nucleus - Hab-I Habenulo-interpeduncular tract - Hem. Cerebral hemisphere - Hip. Hippocampus - Hyp.S. Hypothalamic sulcus - H-th. Hypothalamus - Hyp.C. Hypothalamic cell cord - I.c. Indernal carotid artery - Is. Isthmic segment - Is.n. Isthmic nucleus - I.-v.F. Interventricular foramen - LLF Lateral longitudinal fasciculus - Lat.E. Lateral ventricular eminence - L.t. Lamina terminalis - M Mesencephalon - (MI rostral part - M2 caudal part) - Marg. Marginal ridge - MaT Mamillo-tegmental tract - Med.E. Medial ventricular eminence - MLF Medial longitudinal fasciculus - Mes Mesocortex - M.Ev. Mesencephalic evagination - MFB Medial forebrain bundle - MR5 Mesencephlic root of trigeminal nerve - MTB Medial tectobulbar tract - mot. motor - n. Nucleus - Nas. Nasal pit - N.-H. Neurohypophysis - Not. Notochord - Olf. Olfactory fibres - Olf. E. Olfactory eminence - Opt. Optic cup - Opt.G. Optic groove - Opt.V. Optic ventricle - Ot. Otic vesicle (vestibulocochlear pouch) - P.c. Posterior communicating artery - Pr.-H.T. Preoptico-hypothalamotegmental tract - Pr.R. Preoptic recess - Ret.F. Retinal fissure - Rh Rhombomere - Rh.l. Future rhombic lip - SE Mediolateral cell column - S.l. Sulcus limitans - S-th. Subthalamus - T Primordium of tentorium cerebelli - T. cer. Trigeminocerebellar tract - Tel. Telencephalon - T. hem. Torus hemisphericus - v.Th. ventral thalamus - Ve. Vertebral artery - V.cer. Vestibulocerebellar tract - VE medioventral cell column - Vel. Velum transversum. Numbers 1 to 12 indicate cranial nerves - 7i Intermediate nerve. Where cranial nerves and rhombomeres are labelled in the same figure, the latter are in bold-face numbers. The asterisks in Gigs. 1, 2, and 9 mark the junction of rhombencephalon and spinal cord. The bars in figures 1, 2, 3, 9, and 12 represent 0.2 mm Supported by research grant No. HD-16702, Institute of Child Health and Human Development, National Institutes of Health (USA)     

Psychomotor speed in hypertension: effects of reaction time components, stimulus modality, and phase of the cardiac cycle

Hypertension is characterized by cognitive deficits. As evidence for impaired psychomotor speed, including slower reaction times, is mixed, we aimed to provide a detailed investigation of simple reaction time in hypertension. Pre-motor and motor reaction times were measured across the cardiac cycle in 30 hypertensives and 29 normotensives to determine the effects of phasic and tonic blood pressure on performance. Auditory, visual, and tactile simple reaction time tasks were completed with stimuli presented 0, 300, and 600 ms after the R-wave of the electrocardiogram. Reaction times did not differ between hypertensives and normotensives. Although pre-motor reaction times were faster during the late phase than the early phase of the cardiac cycle whereas motor reaction times were unchanged, this effect was similar for hypertensives and normotensives. No sensory-motor deficits were evident in these hypertensives regardless of baroreceptor activity.     

Nasotemporal overlap in the human retina investigated by means of simple reaction time to lateralized light flash

Summary When light flashes are presented laterally simple vocal and manual responses are faster to stimuli in the visual half-field having direct access to the responding hemisphere (an uncrossed reaction) than stimuli which go initially to the nonresponding hemisphere (a crossed reaction). In the latter case an interhemispheric crossing is presumably necessary and so the crossed-minus-uncrossed difference (CUD) can be identified with interhemispheric transmission time. This paradigm was used to investigate the problem of whether or not there is an overlap of ipsi- and contralaterally projecting ganglion cells at the border between nasal and temporal areas of the human retina, resulting in dual representation of the midline in the brain. If such an overlap does exist then presenting stimuli on this region ought to result in an abolition of the CUD since information would be equally available to both hemispheres. Accordingly vocal and manual reaction times to flashes presented at 1/2, 1, 2, and 4 deg of visual angle were measured. In both cases a consistent CUD was found and this was present at all four points. These results are interpreted as arguing against the existence of overlap in man though some alternative possibilities are discussed.Supported by the British Council and the European Science Foundation by means of twinning grants with the Universities of Pisa and Parma, Italy     

Simple reaction times and performance in the detection of visual stimuli of patients with diabetes

Simple reaction times (SRT) to visual stimuli were investigated through reactions to computer simulations of changes of traffic lights. The performance in the detection of visual stimuli, implying decision processes, was also assessed using the two alternative forced choice (2AFC) method. Subjects were patients affected by diabetes type 2, and observers without diabetes. Results indicated that mean SRT was longer in the group of diabetic patients but was not correlated with age, diabetes duration or fasting glucose. The performance index (d′) was correlated with age and with diabetes duration. Unexpectedly, the correlation between fasting glucose and d′ was not negative.     

Contralateral and ipsilateral motor activation in visual simple reaction time: a test of the hemispheric coactivation model

Motor potentials contralateral versus ipsilateral to the responding hand were examined in a visual simple reaction time (RT) experiment in order to test the hemispheric coactivation model of Miller (Cogn Psychol 49:118-154, 2004). Visual stimuli were presented on the left side of fixation, on the right side, or on both sides, and in the RT task participants had to respond as quickly as possible to the onset of any stimulus. The same stimulus displays were also presented in a counting task, for which participants had merely to count the stimuli. Hemisphere-specific movement-related potentials contralateral and ipsilateral to the responding hand were isolated by subtracting count-task ERPs from RT-task ERPs. Consistent with the hemispheric coactivation model, there was evidence of movement-related ipsilateral positivity as well as contralateral negativity, suggesting that the motor areas of both hemispheres contribute to response initiation in simple RT. The distinction between contralateral and ipsilateral motor activation appears useful in clarifying the roles of the two hemispheres in response initiation.     

Simple and complex reaction time measurement A preliminary evaluation of new approach and diagnostic tool

Investigations of reaction time have been employed in various medical specialties as well as psychology. Although numerous tools have been employed, a universal diagnostic tool has yet to be developed in meeting the requirements of all specialties. Therefore, based on the assumptions of the test theory, we developed a new diagnostic tool, a designed program, designated as Reactor. Subsequent to its implementation in Visual Basic for application and MS Access, Reactor was initially estimated in a group of students. Preliminary evaluation of the Reactor has revealed that it is an innovative and useful diagnostic tool in compliance with the physiological model of reaction time in humans.     

The human brain at stage 17, including the appearance of the future olfactory bulb and the first amygdaloid nuclei

Summary The growth of the cerebral hemispheres rostrally and caudodorsally brings about a deepening of the interlongitudinal fissure, in which blood capillaries for the future choroid plexus develop. Accumulation of mesenchyme basally presages the formation of the nasal septum. The olfactory bulb and tubercle become outlined. The three main areas of the telencephalon, future archi-, paleo-, and neocortex, can be recognized. The amygdaloid body, which is related to the medial ventricular eminence, contains either one or two nuclei. Nerve fibres from the olfactory tubercle arrive and pass through the amygdaloid area. The first indication of a septal nucleus is recognizable. The lateral ventricular eminence is present but not pronounced. The hemispheric stalk joins the cerebral hemispheres to the ventral thalamus and to the diencephalic part of the medial ventricular eminence. The beginning of the future choroid plexus consists in the formation of blood vessels and necrotic changes in the roof of the telencephalon medium and in rostral growth of the anterior choroid artery. Necrotic processes in the future choroid epithelium are now localized at the periphery of the still multilaminar tissue. The sulcus medius and zona intrathalamica delimit the dorsal from the ventral thalamus. The dimesencephalic borderline passes through the commissural fibres in the roof: the rostral part of the commissure is the posterior commissure, the caudal part, the commissure of the superior colliculi. In the mesencephalon, the red nucleus has a laterorostral position with regard to the nucleus of the oculomotor nerve. The cells of the locus coeruleus are well distinguishable. The gustatory fibres begin to separate from the common afferent tract as the tractus solitarius. Inferior and superior salivatory nuclei are delineated.Abbreviations Aff Common afferent tract - A.-H. Adenohypophysial pouch - Amyg. Area of the future amygdaloid body (1, cortical; 2, second nucleus) - ant.ch. Anterior choroid artery - Aq. Aqueduct - Bas. Basilar artery - bm.S. Basal mesencephalic sulcus - e.B. External cerebellar bulge - i.B. Internal cerebellar bulge - Cer. Cerebellum - Ch. Chiasmatic plate - Comm. Commissural plate - XP Posterior commissure - X3 Commissure of the oculomotor nerves - X4 Commissure of the trochlear nerves - X s.C. Commissure of the superior colliculi - sm.X. Supramamillary commissure - so.X. Supraoptic commissure - Cr. Terminal-vomeronasal neural crest - D Caudalmost rhombomere - De Area dentata - D-t S. D1-telencephalic sulcus - Di. Diencephalon - d.F. dorsal funiculus - d.Th. Dorsal thalamus - E. Area epithelialis - End. Endolymphatic duct - Ep. Epiphysis - Hab. Habenular nucleus - Hem. Cerebral hemispheres - Hyp.S. Hypothalamic sulcus - H.-th. Hypothalamus - Hip. Hippocampus - Hyp.C. Hypothalamic cell cord - Is. Isthmic segment - Is.n. Isthmic nucleus - I.v.F. Interventricular foramen - Lat.E. Lateral ventricular eminence - LLF Lateral longitudinal fasciculus - L.t. Lamina terminalis - L.F. Longitudinal fissure - M. Mesencephalon - M1 rostral part - M2 caudal part - Marg. Marginal ridge - Med.E. Medial ventricular eminence - MFB Medial forebrain bundle - MLF Medial longitudinal fasciculus - Mes. Mesocortex - M.Ev. Mesencephalic evagination - MR5 Mesencephalic root of trigeminal nerve - mot. Motor - n. Nucleus - Nas. Nasal sac - N.-H. Neurohypophysis - Not Notochord - Olf.b. Olfactory bulb - Olf.E. Olfactory eminence - Olf.t. Olfactory tubercle - Opt. Optic cup - Opt.G. Optic groove - Ot. Otic vesicle (vestibulochochlear pouch) - Pl. Posterolateral fissure - Pr.R. Preoptic recess - Rh Rhombomere - Rh.l. Rhombic lip - Ru. Red nucleus - SE Mediolateral cell column - Sept. Septum medullae - n.s.i. Interior salivatory nucleus - n.s.s. Superior salivatory nucleus - Sol. Ti. solitarius - S.l. Sulcus limitans - St. Optic stalk - S-th. Subthalamus - S-th.n. Subthalamic nucleus - T Primordium of tentorium cerebelli - Teg. Tegmentum - Tel. Telencephalon - Tel.m. Telencephalon medium - v.Th. Ventral thalamus - V.cer. Vestibulocerebellar tract - VE Visceral efferent (medioventral) cell column - Vel. Velum transversum - VLF Ventral longitudinal fasciculus. Numbers 1 to 12 indicate cranial nerves; 7i Nervus intermedius. Where cranial nerves and rhombomeres are labelled in the same figure, the latter are in bold-face numbers. The bars in Figs. 2, 3, 6, and 7 represent 0.2 mm Supported by research grant No. HD-16702, Institutes of Child Health and Human Development, National Institutes of Health (USA)     

Effect of focal cerebellar lesions on procedural learning in the serial reaction time task

Prior studies have shown that procedural learning is severely impaired in patients with diffuse cerebellar damage (cortical degeneration) as measured by the serial reaction time task (SRTT). We hypothesize that focal cerebellar lesions can also have lateralized effects on procedural learning. Our objective was to assess the effects of focal cerebellar lesions in procedural learning as measured by the SRTT. We studied 14 patients with single, unilateral vascular lesions in the territory of the posterior-inferior or superior cerebellar artery, who were compared with ten age- and sex-matched controls in a one-handed version of the SRTT. Patients with lesions at any other level of the brain or posterior fossa were excluded by cranial magnetic resonance imaging. Our results show that patients do not acquire procedural knowledge when performing the task with the hand ipsilateral to the lesion, but show normal learning with the contralateral hand. No correlation was found with the side, size, or vascular territory of the lesion. We conclude that procedural learning is impaired in hemispheric cerebellar lesions and involves only the hand ipsilateral to the lesion, which suggests a critical role for the cerebellum and/or crossed cerebellar-prefrontal connections in this type of learning. Received: 1 July 1997 / Accepted: 4 November 1997     

Evidence for interhemispheric motor-level transfer in a simple reaction time task: an EEG study

 Simple visuomanual reaction time tasks require interhemispheric communication when stimuli are presented in the hemifield opposite the responding hand. Although confirmed in many studies, it is still a matter of debate when, at what functional level and at what site this interhemispheric transfer takes place. To address these questions, we recorded event-related potentials (ERPs) in 12 healthy subjects performing such a task and analyzed the data using techniques based on topographic ERP map characteristics. A method which has proved useful for associating ERP map configurations of different time periods with functional states of the brain was supplemented by a source localization procedure. The results suggest that transfer occurs late in time, on a functional motor level and at frontal sites, at least for left-to-right interhemispheric direction of transfer. Received: 31 July 1998 / Accepted: 11 December 1998     

The coordination of eye, head, and arm movements during rapid gaze orienting and arm pointing

This study aimed to investigate the coordination of multiple control actions involved in human horizontal gaze orienting or arm pointing to a common visual target. The subjects performed a visually triggered reaction time task in three conditions: (1) gaze orienting with a combined eye saccade and head rotation (EH), (2) arm pointing with gaze orienting by an eye saccade without head rotation (EA), and (3) arm pointing with gaze orienting by a combined eye saccade and head rotation (EHA). The subjects initiated eye movement first with nearly constant latencies across all tasks, followed by head movement in the EH task, by arm movement in the EA task, and by head and then arm movements in the EHA task. The differences of onset times between eye and head movements in the EH task, and between eye and arm movements in the EA task, were both preserved in the EHA task, leading to an eye-to-head-to-arm sequence. The onset latencies of eye and head in the EH task, eye and arm in the EA task, and eye, head and arm in the EHA task, were all positively correlated on a trial-by-trial basis. In the EHA task, however, the correlation coefficients of eye–head coupling and of eye–arm coupling were reduced and increased, respectively, compared to those estimated in the two-effector conditions (EH, EA). These results suggest that motor commands for different motor effectors are linked differently to achieve coordination in a task-dependent manner.     

Somatotopic organization along the central sulcus, for pain localization in humans, as revealed by positron emission tomography

Regional cerebral blood flow was measured with positron emission tomography (PET) in six healthy volunteers at rest and during experimentally induced, sustained cutaneous pain on the dorsum of the right hand or on the dorsum of the right foot. Pain was inflicted by intracutaneous injection of capsaicin, providing a mainly C-fibre nociceptive stimulus. Statistical analysis showed significant activations along the central sulcus (SI) area when comparing pain in the hand to pain in the foot. Separate comparison of both pain states to a baseline revealed different locations along the central sulcus for hand pain and foot pain. The encountered differences are consistent with what is previously known about the somatotopics of non-painful stimuli. When comparing painful stimuli to baseline, the contralateral anterior cingulate gyrus, the ipsilateral anterior insular cortex and the ipsilateral prefrontal cortex were implicated. The results are consistent with an involvement of SI in the spatial discrimination of acute cutaneous pain. Received: 17 October 1996 / Accepted: 12 May 1997