Main Effect Of Task Research Articles

Task Matters: Influence of Different Cognitive Tasks on Cognitive-Motor Interference During Dual-Task Walking in Chronic Stroke Survivors

Background: The impact of unilateral brain damage, such as that caused by stroke, on the interaction between higher cognitive functions and walking remains uncertain. We compared cognitive-motor interference (CMI) during dual-task (DT) walking between chronic stroke survivors and young adults performing explicitly different cognitive tasks. Methods: Ten community-dwelling chronic stroke survivors and 10 young adults performed 3 cognitive tasks – visuomotor reaction time (VMRT), serial subtraction (SS), and Stroop test (STR) – while sitting and walking. Gait velocity was recorded using an electronic walkway. Cognitive variables included reaction time and number of correct responses. Motor and cognitive costs were computed. Results: DT walking led to significant declines in motor and cognitive performance. Significant main effect of task (P < .01) and group (P < .01) was observed for motor cost. The stroke group showed highest motor cost for SS task, whereas the young group showed highest motor cost for STR task (Group × Task interaction, P < .05). Although cognitive costs for both groups was highest for VMRT and lowest for STR tasks, cognitive cost for SS task was significantly greater for the stroke group compared with the young group (Group × Task interaction, P < .05). Conclusions: CMI pattern in chronic stroke survivors differs significantly with type of cognitive task. Gradual cognitive decline with chronicity of condition might have a role in altering the CMI pattern in this population. Future studies of DT interventions for stroke survivors might benefit from incorporating working memory tasks in their protocols.

Eye-movement study during visual search in Chinese children with developmental dyslexia.

Developmental dyslexia (DD) is a disorder in which children with normal intelligence and sensory abilities show learning deficits in reading. Abnormal eye movements have been found in DD. However, eye-movement abnormalities during visual search among Chinese children with DD remain unknown. We aimed to identify the eyemovement characteristics and search efficiency of Chinese children with DD during visual search for targets of different conceptual categories, under same-category conditions. We compared 32 Chinese dyslexic children and 39 non-dyslexic children in visual search tasks, which were assessed using EyeLink II High-Speed Eye Tracker (SR Research Ltd., Canada). Letters, single Chinese characters, digits, Chinese phrases, figures and facial expressions were used as stimuli. Targets were similar to distractors in meaning, phonology and/or shape. A main effect of task on visual search scores and all eye-movement parameters were found. Search scores, average saccade amplitude and saccade distance were significantly smaller in the DD group than in the controls. An interaction between group and task was found for pupil diameter. Unlike normal readers, children with DD had a reduction in the visual attention span and search accuracy. Besides, children with DD could not increase their mental workload with increase in task difficulty. The conceptual category of the stimulus materials significantly impacts search speed, accuracy and eye-movement parameters.

IS 47. Frequency-dependent boosting of fluid intelligence during weak prefrontal alternate current stimulation

Background Modulation of ongoing brain activity through transcranial direct and alternate current stimulation have been already demonstrated, using both steady state cortical excitability and task-related motor performances as final outcome indexes. The opportunity to modulate, i.e. enhance or inhibit, higher level cognitive abilities in the same way is an intriguing scenario, especially for a cognitive rehabilitation perspective, although no evidences have been provided so far. Objective To originally investigate the possibility to modulate abstract reasoning and logical abilities through transcranial alternate current stimulation (tACS), 15 healthy subjects, naive to tACS, underwent a Raven progressive matrices-alike cognitive task, composed by 60 randomized stimuli divided into 4 increasing difficulty levels (namely “1”, “2”, “ 3 Relations ” and “ Logic ” matrices). Five parallel version of the task have been created using SANDIA software and used during 5 randomized separate tACS sessions (5/10/20/40 Hz/sham at 1 mA stimulation intensity), carried out using a bipolar montage (active electrode on left middle frontal gyrus, vertex reference). As a control task, additional reaction times (RTs) were measured throughout the experimental sessions, by using a low-cognitive load odd/even pc-based task. Methods The relationship between performance and the predictors of interest, i.e. tACS (sham/5/10/20/40 Hz) and kind of test (LOGIC and 1/2/3 RELATIONS) was investigated through gamma (for reaction time) and logistic (for accuracy) regressions. Results A main effect of Task on both accuracy ( X 2 = 3668.5, p X 2 = 424.6, p X 2 = 13.6, p X 2 = 0.3, n.s). Consistently, the presence of interaction between tACS and task for RTs (40 Hz; X 2 = 97.7, p X 2 = 125.6, p Conclusions results originally show a possible online boosting of higher order cognitive abilities using tACS. The frequency-dependent gamma-band tACS effect on RTs offers an interesting hypothesis about a cognitive flexibility improvement during high loading tasks (3 relations and logic), possibly induced by an entrainment of gamma stimulation. Such an entrainment might cause an increase of gamma bursts occurrence typically observed during problem solving.

Dual-Task Effect on Gait Balance Control in Adolescents With Concussion

ObjectiveTo prospectively and longitudinally examine how concussion affects gait balance control in adolescents during single- and dual-task walking. DesignCohort, prospective, repeated-measures design. SettingMotion analysis laboratory. ParticipantsAdolescents (N=20) identified as suffering a concussion were matched with healthy control subjects (N=20) and tested 5 times across a 2-month period after injury. InterventionsNot applicable. Main Outcome MeasuresGait temporal-distance parameters included average walking speed, step length, and step width; whole body center of mass (COM) parameters included medial/lateral displacement and peak COM medial/lateral and anterior velocities; dual-task cost, which was defined as percent change from single- to dual-task conditions; and Stroop test accuracy. ResultsNo between-group differences were observed for step length and step width. The dual-task cost for average walking speed for subjects with concussion was greater than control subjects across the 2-month testing period (main effect of group P=.019), as was the dual-task costs for peak anterior COM velocity (main effect of group P=.017) and total COM medial/lateral displacement (main effect of group P=.013). The total COM medial/lateral displacement (group × task interaction P=.006) and peak COM medial/lateral velocity (main effect of group P=.027; main effect of task P=.01) were significantly greater in subjects with concussion compared with control subjects during dual-task walking. Subjects with concussion were significantly less accurate than controls on the Stroop test (main effect of group P=.004). ConclusionsThe findings suggest that concussion affects the ability of adolescents to control body posture during gait up to 2 months after injury. Furthermore, dual-task paradigms may provide additional useful information in the clinical assessment and recovery of concussion.

Cerebral responses to vocal attractiveness and auditory hallucinations in schizophrenia: a functional MRI study

Impaired self-monitoring and abnormalities of cognitive bias have been implicated as cognitive mechanisms of hallucination; regions fundamental to these processes including inferior frontal gyrus (IFG) and superior temporal gyrus (STG) are abnormally activated in individuals that hallucinate. A recent study showed activation in IFG-STG to be modulated by auditory attractiveness, but no study has investigated whether these IFG-STG activations are impaired in schizophrenia. We aimed to clarify the cerebral function underlying the perception of auditory attractiveness in schizophrenia patients. Cerebral activation was examined in 18 schizophrenia patients and 18 controls when performing Favorability Judgment Task (FJT) and Gender Differentiation Task (GDT) for pairs of greetings using event-related functional MRI. A full-factorial analysis revealed that the main effect of task was associated with activation of left IFG and STG. The main effect of Group revealed less activation of left STG in schizophrenia compared with controls, whereas significantly greater activation in schizophrenia than in controls was revealed at the left middle frontal gyrus (MFG), right temporo-parietal junction (TPJ), right occipital lobe, and right amygdala (p < 0.05, FDR-corrected). A significant positive correlation was observed at the right TPJ and right MFG between cerebral activation under FJT minus GDT contrast and the score of hallucinatory behavior on the Positive and Negative Symptom Scale. Findings of hypo-activation in the left STG could designate brain dysfunction in accessing vocal attractiveness in schizophrenia, whereas hyper-activation in the right TPJ and MFG may reflect the process of mentalizing other person's behavior by auditory hallucination by abnormality of cognitive bias.

Visual-vestibular stimulation influences spatial and non-spatial cognitive processing

This study investigated the impact of visual-vestibular stimulation on performance of an auditory information processing task in young and older adults. Performance on a spatial choice reaction time task was compared to performance on a non-spatial choice reaction time task. The tasks were performed during simultaneous rotational and moving visual stimulation. The non-spatial task was an auditory frequency discrimination task while the spatial task was a right-left lateralization task. Visual and vestibular conditions consisted of a non-movement baseline, sinusoidal earth-vertical axis rotation (EVAR) in darkness, off-vertical axis rotation (OVAR) in darkness at a constant velocity, OVAR in darkness with a sinusoidal profile, EVAR with a lighted visual surround, constant velocity optokinetic stimulation, and sinusoidal optokinetic stimulation. Baseline reaction times were subtracted from reaction times during each stimulus condition to yield "task cost", which was analyzed statistically. Subjects were healthy young (n=20; 24 ± 2.7 yrs; 10F) and older (n=29; 73 ± 6.0 yrs; 18F) adults. Results indicated that task cost was affected by the visual-vestibular condition and a task x condition interaction. There was no main effect of task or age group and no significant interaction with age. Otolithic stimulation and visual stimulation were associated with greater task cost compared to semicircular canal stimulation. Combining semicircular canal with otolithic or visual stimulation had no additional effect beyond otolithic or visual stimulation alone. This pattern of task cost being larger for otolith or visual vs. semicircular canal stimulation was found for both the spatial and non-spatial tasks. The significant interaction between condition and task type revealed that the task cost for the spatial task was larger than the task cost for the non-spatial task during visual conditions but not during non-visual conditions although the visual and non-visual conditions were not entirely comparable. This study suggests that interference of vestibular stimulation with cognitive processing is especially prominent for otolithic and visual stimulation although the strength of the various visual-vestibular stimuli may not have been uniform. Also, spatial tasks are more affected than non-spatial tasks during visual stimulation and interference between vestibular stimulation and cognitive processing is not age dependent for these relatively easy tasks.

Graphophonological processes in dyslexic readers of French: A longitudinal study of the explicitness effect of tasks

Given the well-acknowledged phonological deficit found in dyslexic children, this study was aimed at investigating graphophonological processes in dyslexic readers of French over a 1-year period. Among the different types of phonological processing can be distinguished those related to phonological awareness based on knowledge of the oral language and graphophonological processes based on correspondences between the oral and the written language. In this study, we evaluated graphophonemic and graphosyllabic processes using, in each case, two different tasks varying in the degree of cognitive constraint associated with the task (CC- vs CC+). Twenty 11 year-old dyslexic students were compared with younger normal-readers of the same reading level (RA, n=26) and to normal-readers of the same age (CA, n=24). Two variables were considered in the analyses: accuracy and response latency. Results show that dyslexic readers do process written items at the graphophonological level. Also, results indicate main effects of task (CC- vs CC+), time (T1 vs T2), and group (DYS vs RA vs CA). In general, dyslexic participants' performances are comparable to those of RA and differ from those of CA.

The Effect of Task in Deaf Readers' Graphophonological Processes: A Longitudinal Study

This article reports on an investigation of graphophonological processes in deaf readers of French over a 1-year period. Deaf readers are known to have a phonological deficit compared to hearing peers, and conclusions from studies on this question are often conflicting. Among the different types of phonological processing, we can identify graphophonological processes based on correspondences between the oral and the written language. In this investigation, we evaluated graphophonemic and graphosyllabic processes using, in each case, two different tasks varying in their degree of cognitive constraints (CC- vs. CC+). Nineteen 11 year-old deaf students were compared to younger normal readers of the same reading level (RA, n = 17) and to normal readers of the same age (CA, n = 20). Two variables were considered in the analyses: accuracy and response latency. Results show that deaf readers do process written items at the graphophonological level and that graphophonological processes are related to reading ability. Also, results indicate main effects of task (CC- vs. CC+), time (T1 vs. T2), and group. In general, deaf participants' performances are comparable to those of RA and differ from those of CA. Results are discussed within the framework of the study of phonology in deaf readers and its relation to reading acquisition.

Temporal Anticipation Under Cognitive Stress

The ability to produce performances at highest level under physically and emotionally demanding conditions underline the worth of a sportsperson. These stressful conditions places demands on the cognitive resources of the sportsperson; especially in anticipatory actions that require the allocation of cognitive resources. This study investigated the effects of cognitive stress on the temporal anticipation of a timing motor task. A repeated measures design was applied with two independent variables; cognitive stress and levels of difficulty, which included easy, intermediate and difficult. Study participants were 18 male and 18 female undergraduates of the Physical Education programme of Universiti Putra Malaysia. The experimental task involved performing a timing motor task across the three levels of difficulty, under two conditions as follows: (i) without cognitive stress, and (ii) under cognitive stress. Cognitive stress was induced via the continuous subtraction of two from a two-digit number. Participants performed the task individually and the sequence of the experimental task was counter-balanced. A two-way within subject ANOVA was performed to ascertain the effects of cognitive stress on the temporal anticipation of the timing motor task. Data yielded significant difference in means for the stress main effect [Λ = .64, F (1.35) = 19.89, p < 0.05]; and the task main effect [Λ = .84, F (2, 34) = 3.35, p < 0.05]. Post hoc comparisons produced a significant difference in the means of the performance of the timing motor task at all three levels of difficulty. Data showed that cognitive stress had an effect on the temporal anticipation of the timing motor task. These results are explained from attentional and the neuromotor noise perspectives. It was concluded that the significant difference in the performance of the experimental task was due to the competition for intentional resources and the decrease of the signal to noise ratio due to cognitive stress.

Chest Wall Kinematics during Speech Breathing in Tracheoesophageal Speakers

The purpose of the present study was to determine how tracheoesophageal (TE) speakers manipulate the chest wall (rib cage and abdomen) to speak and how respiratory compromise (chronic obstructive pulmonary disease; COPD) and task variables influence those behaviors. The chest wall movements of 11 male TE speakers (5 with COPD and 6 without COPD) were measured during tidal breathing, spontaneous speech, and reading. Repeated-measures multivariate analyses were used to compare breathing behaviors across speech tasks and by respiratory health. Additional repeated-measures multivariate analyses and 1-way analyses of variance were conducted on temporal, aerodynamic, and linguistic measures. There was a significant main effect of task and a significant interaction effect of COPD and task on chest wall movements. Rib cage movements varied by task, whereas abdominal movements were as predicted. There was a significant difference in utterance length by task. There were no main effects of COPD on the chest wall and no significant group differences in utterance length, aerodynamic measures, or intelligibility. The TE speakers were generally accurate in inspiring at appropriate linguistic boundaries. The results suggest that there is robust control for speech breathing following laryngectomy, but that there is also increased effort within the chest wall. Implications for future research considerations are discussed.

Knee Kinematic Coupling in Males and Females: Open and Closed-Chain Tasks

The purpose of this study was to compare the magnitude of knee kinematic coupling between genders and among open- and closed-chain tasks. A secondary purpose was to compare the consistency of knee kinematic coupling between genders and among open- and closed-chain tasks. Vector-coding methods were used to quantify coupling in the sagittal and transverse planes of the knee between full extension and 20 degrees of flexion as 10 males and 10 females walked, ascended and descended stairs, and performed a passive pendulum leg drop. An ANOVA showed no main effect of gender. There was a main effect of task, where coupling during the stance phase of walking was significantly greater than each of the other tasks. Intraclass correlation values suggested that males were slightly more consistent than females. A general lack of divergence between genders may be related to the tasks analyzed in this study. It is possible that more strenuous tasks may elicit larger differences.

Lung Volumes Used during Speech Breathing in Tracheoesophageal Speakers

The purpose of this study was to determine how tracheoesophageal (TE) speakers manipulate lung volumes to meet speech demands and how respiratory compromise (chronic obstructive pulmonary disease [COPD]) and task variables influence these behaviors. The lung volumes of 9 male TE speakers (4 with COPD, 5 without) during tidal breathing, spontaneous speech, and reading were investigated. Repeated-measures multivariate analyses of variance were used to compare lung volumes and utterance length across speech tasks and by respiratory health. A one-way analysis of variance was used to compare aerodynamic measures and intelligibility by COPD diagnosis. There was a significant main effect of task and a significant interaction effect of COPD and task on lung volumes at initiation and termination of speech. The TE speakers terminated speech exclusively below the resting expiratory level (REL) in both speech tasks because of elevated RELs, which are often present after laryngectomy. There were no main effects of COPD on any lung volume measures and no significant group differences in utterance length, aerodynamic measures, or intelligibility. Intelligibility and aerodynamic measures were not influenced by lung volumes and were comparable to findings of previous research. Speaking past the REL might be a compensation to optimize expiratory control for speech in a compromised system and a marker for the increased effort often anecdotally described by TE speakers.

Cognitive control of a simple mental image in patients with obsessive–compulsive disorder

The nature of obsessions has led researchers to try to determine if the main problem in obsessive–compulsive disorder (OCD) is impaired inhibitory control. Previous studies report that the effort to suppress is one of the factors that increase the frequency of obsessive thoughts. Based on these results and those of the present study that suggest inferior parietal lobe (IPL) abnormality in OCD and findings of a recent study that reported the importance of the right posterior parietal cortex in cognitive control of a simple mental image, the present cognitive control paradigm study aimed to determine whether there is a difference in brain dynamics between OCD patients and non-obsessive controls while performing tasks that necessitate cognitive control of a simple mental image, and whether the right posterior parietal region is one of the regions in which a difference in activity between the OCD patients and controls would be observed. Functional brain imaging was performed while the participants attempted to suppress, imagine, or manipulate a mental image. The general linear model showed that there was a main effect of group and main effect of task. Accordingly, in all contrasts (suppression minus free-imagination, erasing minus free-imagination, and imagination minus free-imagination), the right IPL, right posterior cingulate cortex, and right superior frontal gyrus activity were lower in the OCD patients than in the healthy controls. These results and the observed correlations between activity levels, and symptom and subjective performance scores are discussed. In conclusion, the results of the present study and those of previous studies suggest that the main problem in OCD might be difficulty activating the right frontoparietal networks during tasks that require cognitive control, which might result in the intrusiveness of obsessive thoughts.

The Neural Basis of Body Form and Body Action Agnosia

Visual analysis of faces and nonfacial body stimuli brings about neural activity in different cortical areas. Moreover, processing body form and body action relies on distinct neural substrates. Although brain lesion studies show specific face processing deficits, neuropsychological evidence for defective recognition of nonfacial body parts is lacking. By combining psychophysics studies with lesion-mapping techniques, we found that lesions of ventromedial, occipitotemporal areas induce face and body recognition deficits while lesions involving extrastriate body area seem causatively associated with impaired recognition of body but not of face and object stimuli. We also found that body form and body action recognition deficits can be double dissociated and are causatively associated with lesions to extrastriate body area and ventral premotor cortex, respectively. Our study reports two category-specific visual deficits, called body form and body action agnosia, and highlights their neural underpinnings.

Effects of shifting perspective of the self: An fMRI study

When looking to our reflection, or moving a video-game character, we see our own movement preformed by an agent which is physically separated from our body. Yet, we consider the agent to be ourself. Using fMRI, we sought to explore the neural underpinnings of disembodiment, the cognitive mechanism under which the properties of the self are projected away from the boundaries of one’s own body towards an external entity. Seventeen participants watched a video-game in which three players threw each other a ball. Subjects’ key-press could either be synchronous or asynchronous with one of the players’ action (TASK: Agency vs. Control). The game was shown from one of four viewpoints which could either be fixed or change every trial (VIEWS: Fixed vs. Changeable). Consistent with previous studies, the left insula was activated when the agent’s movements were synchronous with those of the participants (main effect of TASK, p<0.05, SVC). The analysis of the interaction TASK⁎VIEWS revealed activation (p<0.05, corrected) of the right parieto-temporal-occipital (PTO) junction when the agent whose movements were synchronous to the participants was processed in a spatial position each time different with respect to the preceding trials. Our findings implicate the right PTO junction in assigning one’s own movements to an agent which is physically independent of oneself. They also suggest that the ability to disembody, and thereby objectify, bodily or mental states concerning the self is common to all experimental paradigms which led to an activation of the PTO junction.

The effect of camera viewing angle on posture assessment repeatability and cumulative spinal loading

Video-based task analysis in the workplace is often limited by equipment location and production line arrangement, therefore making it difficult to capture the motion in a single plane. The purpose of this study was to investigate the effects of camera placement on an observer's ability to accurately assess working postures in three dimensions and the resultant influence on the reliability and repeatability of calculated cumulative loading variables. Four video cameras were placed at viewing angles of 0°, 45°, 60° and 90° to the frontal plane, enabling the simultaneous collection of views of four lifting tasks (two symmetric and two asymmetric). A total of 11 participants were trained in the use of the 3DMatch 3-D posture matching software package (developed at the University of Waterloo) and were required to analyse 16 lifting trials. Four of the participants were randomly selected to return within 72 h and repeat the analysis protocol to test intra-observer repeatability. Posture matching agreement between camera views was higher when the body segments had a minimal range of motion during the task. There was no significant participant main effect; however, there was a significant (p < 0.05) task main effect. Intraclass correlation coefficients (ICC) were calculated to assess the between day reliability. Compression, reaction anterior shear and extension moment were all found to have excellent reliability (ICC > 0.75). Joint anterior shear and joint posterior shear both provided fair to good reliability (0.4 > ICC < 0.75). Overall, the impact of the camera viewing angle on an observer's ability to match working postural exposure was found to be small.

White matter abnormalities and brain activation in schizophrenia: A combined DTI and fMRI study

Diffusion tensor imaging (DTI) studies of schizophrenia have revealed white matter abnormalities in several areas of the brain. The functional impact on either psychopathology or cognition remains, however, poorly understood. Here we analysed both functional MRI (during a working memory task) and DTI data sets in 18 patients with schizophrenia and 18 controls. Firstly, DTI analyses revealed reductions of fractional anisotropy (FA) in the right medial temporal lobe adjacent to the right parahippocampal gyrus, likely to contain fibres of the inferior cingulum bundle, and in the right frontal lobe. Secondly, functional MRI revealed prefrontal, superior parietal and occipital relative hypoactivation in patients with the main effect of task. This was accounted for by reduced prefrontal activation during the encoding phase of the task, but not during maintenance or retrieval phases. Thirdly, we found a direct correlation in patients between the frontal FA reduction (but not medial temporal reductions) and fMRI activation in regions in the prefrontal and occipital cortex. Our study combining fMRI and DTI thus demonstrates altered structure-function relationships in schizophrenia. It highlights a potential relationship between anatomical changes in a frontal–temporal anatomical circuit and functional alterations in the prefrontal cortex.

An fMRI study of the binding of audio-visual information: the dissociation between object and space processing

Recent neuroimaging research highlighted the contribution of different heteromodal cortical regions during various forms of crossmodal binding. Interestingly, crossmodal effects during audiovisual speech and object recognition have been found in the superior temporal sulcus (STS), while crossmodal effects during the execution of spatial tasks have been found over the intraparietal sulcus (IpS), suggesting an underlying “what/where” segregation. In this fMRI study, we investigated if a such “what/where” functional segregation, similar to the one observed for both visual and auditory cortical processing, exists in the crossmodal domain, when visual and auditory stimuli have to be matched in order to perform either a recognition or a localization task. In order to directly compare the specific involvement of these two heteromodal regions, we scanned ten male right handed subjects during the execution of two crossmodal matching tasks. Participants were simultaneously presented with a black and white picture, chosen from the Snodgrass and Vanderwart’s set, and an environmental sound, selected from a free internet archive set. The pictures and the sounds could be presented in either the same or the opposite hemifield and represent either the same or a different object. Subjects were required to report whether the two attended stimuli were matching or mismatching with respect to either spatial position (localization task) or semantic content (recognition task) by pressing two buttons of a response pad. The group analysis showed that the crossmodal localization task elicited more activity than the recognition task in the left and right precuneus, in the right parietal cortex, including the IpS, and in the right superior occipital cortex. Regions responding to the crossmodal recognition task more than to the localization task were found in the inferior occipital gyrus, bilaterally, and in the left lateral temporal cortex, including the anterior part of the STS and the superior temporal gyrus. An individual subject analysis was performed on the left superior temporal sulcus and on the right intraparietal sulcus, in order to take account for the intersubject anatomical variability in the relative location and extension of cortical sulci. The 2 × 2 (TASK × CONGRUENCY) within subject ANOVA confirmed the results of the group analysis, showing a main effect of task in the right IpS [F(1,9) = 14.33, P < 0.005] and in the left STS [F(1,9) = 20.52, P < 0.001] but no effect of congruency. Our results are consistent with a “what–where” functional segregation in the crossmodal audiovisual domain, and suggest the role of the IpS in the binding of “spatial” audiovisual information and of the STS in the binding of “semantic” audiovisual information. The dissociation between object and spatial processing streams seems to be an organizing principle of the cortical functioning.

Action Understanding Requires the Left Inferior Frontal Cortex

Numerous studies have established that inferior frontal cortex is active when hand actions are planned, imagined, remembered, imitated, and even observed. Furthermore, it has been proposed that these activations reflect a process of simulating the observed action to allow it to be understood and thus fully perceived. However, direct evidence for a perceptual role for left inferior frontal cortex is rare, and linguistic or motor contributions to the reported activations have not been ruled out. We used repetitive transcranial magnetic stimulation (rTMS) over inferior frontal gyrus during a perceptual weight-judgement task to test the hypothesis that this region contributes to action understanding. rTMS at this site impaired judgments of the weight of a box lifted by a person, but not judgements of the weight of a bouncing ball or of stimulus duration, and rTMS at control sites had no impact. This demonstrates that the integrity of left inferior frontal gyrus is necessary to make accurate perceptual judgments about other people's actions.

HETERONYMOUS REFLEXES IN THE PRIMARY AGONIST ARE ENHANCED WHEN SUPPORTING AN INERTIAL LOAD.

Purpose/Hypothesis: Previous studies indicate that stretch reflexes in the human upper limb are influenced by the stability of the load supported during an isometric contraction. Our purpose was to assess whether changes in the sensitivity of spinal motor neurons to afferent feedback from accessory muscles contribute to reflex modulation when supporting an inertial load compared with exerting an equivalent force with the limb restrained. Number of Subjects: 13 healthy adults (aged 18–47 years, 9 men) participated in the study. Materials/Methods: Heteronymous reflexes were evoked in the first dorsal interosseus (agonist) and second palmar interosseus (antagonist) muscles by stimulating the median nerve at the wrist (1 ms pulse width; 3–5 s inter-stimulus interval) as subjects performed two motor tasks with the index finger. One task required subjects to exert a constant isometric force by pushing up against a rigid restraint, whereas the other task required subjects to maintain a constant angle at the metacarpophalangeal joint while supporting an inertial load suspended from the finger. Net torque (20% of maximum), the position of the index finger (0 degrees abduction), and the intensity of peripheral nerve stimulation were the same for both tasks. Twenty-four reflex responses were recorded in each muscle using surface or intramuscular electrodes, and the averaged EMG records were compared using a 2-factor ANOVA for repeated measures. Results: Heteronymous reflex responses were observed in 10/13 subjects (77%) for the first dorsal interosseus, but only 2/11 subjects (18%) in the second palmar interosseus. Despite similar tonic EMG of the agonist and antagonist muscles across tasks (P = 0.27), peak amplitudes of the short-latency (SL 28.6 ± 5.6 ms) and long-latency (LL 52.2 ± 3.5 ms) reflexes in the first dorsal interosseus were greater when subjects supported the inertial load (SL = 0.45 ± 0.19 vs. 0.57 ± 0.28 mV; LL = 0.32 ± 0.11 vs. 0.41 ± 0.19 mV; main effect of task P = 0.02). Conclusions: Agonist motor neurons exhibit heightened sensitivity to afferent feedback from median-innervated accessory muscles when controlling the position of an inertial load. Clinical Relevance: Findings indicate that the type of load used in strength and endurance training programs can influence the response of the primary agonist to concurrent activity of accessory musculature.