ERP evidence of attentional somatosensory processing and stimulus-response coupling under different hand and arm postures.

We investigated (1) the effects of divided and focused attention on event-related brain potentials (ERPs) elicited by somatosensory stimulation under different response modes, (2) the effects of hand position (closely-placed vs. separated hands) and arm posture (crossed vs. uncrossed forearms) on the attentional modulation of somatosensory ERPs, and (3) changes in the coupling of stimulus- and response-related processes by somatosensory attention using a single-trial analysis of P300 latency and reaction times. Electrocutaneous stimulation was presented randomly to the thumb or middle finger of the left or right hand at random interstimulus intervals (700-900 ms). Subjects attended unilaterally or bilaterally to stimuli in order to detect target stimuli by a motor response or counting. The effects of unilaterally-focused attention were also tested under different hand and arm positions. The amplitude of N140 in the divided attention condition was intermediate between unilaterally attended and unattended stimuli in the unilaterally-focused attention condition in both the mental counting and motor response tasks. Attended infrequent (target) stimuli elicited greater P300 in the unilaterally attention condition than in the divided attention condition. P300 latency was longer in the divided attention condition than in the unilaterally-focused attention condition in the motor response task, but remained unchanged in the counting task. Closely locating the hands had no impact, whereas crossing the forearms decreased the attentional enhancement in N140 amplitude. In contrast, these two manipulations uniformly decreased P300 amplitude and increased P300 latency. The correlation between single-trial P300 latency and RT was decreased by crossed forearms, but not by divided attention or closely-placed hands. Therefore, the present results indicate that focused and divided attention differently affected middle latency and late processing, and that hand position and arm posture also differently affected attentional processes and stimulus-response coupling.

Effects of a single bout of walking on psychophysiologic responses and executive function in elderly adults: a pilot study.

BACKGROUND: The purpose of this study was to examine the effects of a single bout of walking on mood, psychophysiologic responses, and executive function in elderly adults. METHODS: Twenty healthy, elderly adults (10 women and 10 men; mean age 70.50 ± 3.4 years) participated in this study. Mood, as assessed by the Profile of Mood States, and salivary α-amylase activity were examined before and after walking. Executive functions were also evaluated by the Wisconsin Card Sorting Test. RESULTS: Negative feeling scores such as tension-anxiety, anger-hostility, and confusion significantly improved after walking. No significant differences were found for either salivary α-amylase activities or Wisconsin Card Sorting Test scores before and after walking. However, the changes in salivary α-amylase activity before and after walking correlated positively with the number of total errors and perseverative errors of Nelson in the Wisconsin Card Sorting Test. CONCLUSION: These results suggest that moderate exercise, such as self-paced one-time walking, induces beneficial psychologic effects in elderly adults. Meanwhile, the significant increase in salivary α-amylase activity after walking might temporarily cause deterioration of executive function.

Dual-task repetition alters event-related brain potentials and task performance.

OBJECTIVE: We examined the modulation of event-related brain potentials (ERPs) and the accuracy of sensori-motor coordination on short-term repetition of the concurrent performance of a somatosensory discrimination (oddball) task and a visuo-motor tracking task. METHODS: The subjects concurrently performed visuomotor tracking and somatosensory oddball tasks. In the dual-task condition, the subjects performed the visuomotor tracking and somatosensory oddball tasks concurrently for about an hour. In the oddball-only condition, they performed just the oddball task for the same period. RESULTS: Tracking performance improved with task repetition. The amplitude of the P300 elicited by somatosensory stimulation in the oddball-only condition decreased significantly with task repetition, whereas in the dual-task condition, it showed a complex pattern of change. The earlier responses were decreased in amplitude in the dual-task condition compared to the oddball-only condition, and gradually decreased with task repetition in both conditions. CONCLUSIONS: Dynamic changes in ERPs and task performance with dual-task repetition support the idea that dual-task repetition produces changes in resource allocation following the automation of stimulus processing in addition to so-called habituation. SIGNIFICANCE: This study also provides evidence for use of ERP amplitudes as physiological indices of functionally different types of resources.

Modulation of somatosensory processing in dual tasks: an event-related brain potential study.

The amplitudes of the event-related brain potentials (ERPs) have been associated with the amount of attentional resources. The present study investigated whether force production type (increasing or decreasing force) in a visuomotor force tracking task modulates the ERPs elicited in a somatosensory oddball task performed simultaneously, whether stimulus-response coupling assessed by a single-trial analysis of P300 latency is modulated by the concurrent performance of the tasks, and whether dynamic visuomotor coordination rather static coordination is sensitive to the ERP modulation. In the dual-task condition, the subjects tracked a target line moving on the display with another line representing the force generated by the grip of their left hand, while executing the somatosensory oddball task with the right hand. In the oddball-only condition, the oddball task only was performed. The amplitude of the P300 elicited in the oddball task was decreased in the dual-task condition compared with the oddball-only condition, and further decreased in the force-decreasing phase compared with the increasing phase, but was not altered by the concurrently performed isometric contraction. P100, N140, reaction time (RT), and error rate were not influenced by force production type. A correlation analysis of single-trial P300 latency and RT showed that the dual-task condition produced a stronger coupling of the P300 and RT. In summary, different force production types requiring dynamic visuomotor coordination alter a modality-nonspecific late stage of somatosensory processing but have less of an effect on early stages. During the performance of the dual task, stimulus-response coupling in the somatosensory discrimination task becomes stronger to compensate for a lack of resources and/or due to snap decisions owing to sufficient resources.

Long-term motor practice induces practice-dependent modulation of movement-related cortical potentials (MRCP) preceding a self-paced non-dominant handgrip movement in kendo players.

Effects of long-term motor practice on movement-related brain activities were investigated by measuring from the scalp, movement-related cortical potentials (MRCP) associated with self-paced right (dominant) and left (non-dominant) brisk handgrip movements with a 20% maximal voluntary contraction (MVC) in 8 elite kendo players (kendo group) and 8 healthy young adults (control group). The kendo players had engaged in regular practice since childhood. Three components of MRCP were obtained from all subjects. These components relating to the preparation (Bereitschaftspotential: BP and negative slope: NS') and initiation (motor potential: MP) of the movements were compared between the two groups. The BP onset time for a non-dominant handgrip task was significantly earlier in the control group than in the kendo group. Moreover, BP onset time appeared significantly earlier preceding the non-dominant handgrip task as compared with the dominant one only in the control group. Furthermore, MP amplitudes in the kendo group were significantly larger than in the control group. These findings suggest that long-term motor practice affects brain activities, leading to practice-dependent modulations in the cortical areas involved in the preparation and initiation of self-paced non-dominant handgrip movements in kendo players.

Acute effects of aerobic exercise on cognitive function in older adults.

The present study investigated the effects of acute aerobic exercise on cognitive brain functions of older adults. Twenty-four males (12 older and 12 younger adults) performed a modified flanker task during a baseline session (no exercise) and after light and moderate cycling exercise in counterbalanced order on different days while measures of task performance and the P3 component of an event-related brain potential were collected. The results indicated that, for both age groups, reaction time following moderate exercise was shorter relative to the other sessions, and P3 latencies following both light and moderate exercise were shorter compared with the baseline session. In contrast, P3 amplitude increased only following moderate exercise in younger adults. These findings suggest that light and moderate exercises improve cognitive function across the adult lifespan, although the mechanisms underlying the effects of observed acute aerobic exercise on cognitive function may be age dependent.

The interactive effect of exercise intensity and task difficulty on human cognitive processing.

The interactive effect of exercise intensity and task difficulty on human cognitive processing was investigated using the P3 component of an event-related brain potential (ERP). Exercise intensity was established using Borg's rating of perceived exertion (RPE) scale, and task difficulty was manipulated using a modified flanker task comprised of incongruent and neutral trials. Twelve participants (22 to 30 y) performed the flanker task during a baseline session, and again after light (RPE: 11), moderate (RPE: 13), and hard (RPE: 15) cycling exercise. Results indicated that the P3 amplitude increases across task conditions following light and moderate cycling, but not during hard cycling, relative to baseline, suggesting that P3 amplitude may change in an inverted U fashion by as a result of acute exercise intensity. Additionally, the expected delay in P3 latency for incongruent relative to neutral trials was observed during the baseline condition. However, following acute exercise these task condition differences diminished across exercise intensities. Moreover, reaction times following all exercise conditions were shorter when compared to the baseline condition. These findings suggest that P3 latency is more sensitive to task difficulty manipulated by a flanker task than behavioral measures, and P3 latency during trials requiring greater executive control processes might be more sensitive to the effects of acute exercise than tasks requiring minimal effort.

Effects of habitual moderate exercise on response processing and cognitive processing in older adults.

We examined the effects of habitual moderate exercise on central information processing in older individuals using the reaction time (RT) and P3 component of event-related brain potentials (ERP). The present study was designed to assess cognitive function by comparing groups of 20 older individuals (69.20 +/- 1.3 years active group) who regularly engage in moderate physical activity with 20 subjects (66.90 +/- 1.1 years inactive group) who do comparatively little exercise. Subjects performed a somatosensory oddball task composed of pressing a button with their right foot as fast as possible following an electrical stimulus applied to the right index finger, and not responding to an electrical stimulus applied to the left index finger. Electroencephalogram (EEG) was recorded at the frontal (Fz), central (Cz), and parietal (Pz) sites according to the International 10-20 system referenced to linked earlobes. The RT was faster for the active group than for the inactive group, and the P3 amplitude of the active group was significantly larger than that of the inactive group. Moreover, the P3 amplitude for the active group was maximum at Pz and significantly larger than at Fz and Cz, but for the inactive group it was identical between Fz and Pz. The results suggest that habitual moderate exercise exerts positive influences in older adults not only on response processing, but also on cognitive processing.

Load- and cadence-dependent modulation of somatosensory evoked potentials and Soleus H-reflexes during active leg pedaling in humans.

Modulation of transmission in group I muscle afferent pathways to the somatosensory cortex and those to the alpha-motoneuron were investigated during active leg pedaling. Cerebral somatosensory evoked potentials (SEPs) and Soleus (Sol) H-reflexes following posterior tibial nerve stimulation were recorded at four different pedaling phases. The subjects were asked to perform pedaling at three different cadences (30, 45 and 60 rpm with 0.5 kp, cadence task; C-task) and with three different workloads (at 45 rpm with 0.0, 0.5 and 1.0 kp, load task; L-task). In both C- and L-tasks, Sol H-reflexes were modulated in a phase-dependent manner, showing an increase in the power phase and a decrease in the recovery phase. In contrast, the early SEP (P30-N40) components were modulated in a phase-dependent manner when the cadence and load were low. When focusing on the power phases, significant cadence- and load-dependent modulations of the P30-N40 were found, and inversely graded with the cadence and load. The H-reflex was found to be significantly decreased at the highest cadence, i.e., cadence-dependent modulation. In contrast, the H-reflex during the L-task was found to be proportional to the load. The correlation analysis between the size of H-reflex and the amount of background (BG) electromyographic (EMG) activity demonstrated that the H-reflex in the power phase did not depend on the BG EMG in either C- or L-task. These findings suggested that transmission of muscle afferents along the ascending pathways to the cerebral cortex and the spinal cord is independently controlled in accordance with the biomechanical constraints of active pedaling.

Changes in arousal level by differential exercise intensity.

OBJECTIVE: The purpose of the present study was to investigate the influence of exercise intensity on arousal level. METHODS: Twelve subjects (22-33 years) performed a S1-S2 reaction time task consisting of warning stimulus (S1) and imperative stimulus (S2) in a control condition, and again after low, medium, and high intensity pedaling exercises. During this task, contingent negative variation (CNV) and spontaneous electroencephalogram before S1 were measured as indicators for arousal level. RESULTS: CNV amplitude after high intensity pedaling exercise was significantly smaller than after medium pedaling exercise. Compared to the control condition, relative power value of alpha waves increased after the high intensity exercise. CONCLUSIONS: These results suggested that arousal level was reduced after high intensity exercise and reached a state near optimal level after medium intensity exercise. The findings also suggested that changes in CNV amplitude by differences in exercise intensity followed an inverted-U shaped dose response curve. SIGNIFICANCE: The present study supported the view that CNV amplitude and arousal level followed an inverted-U relationship. It is concluded that differences in exercise intensity influenced arousal level.

Resource allocation and somatosensory P300 amplitude during dual task: effects of tracking speed and predictability of tracking direction.

OBJECTIVE: The amount of attentional resources allocated to a task is determined by the intrinsic demands, also denoted as task load or difficulty of the task. Effects of resource allocation on the somatosensory N140 and P300 were investigated in an inter-modal situation using a dual-task methodology. METHODS: Under a dual-task condition, subjects concurrently performed a visuomotor tracking task and a somatosensory oddball task, while they performed just the oddball task under an oddball-only condition. In the tracking task, the subjects tracked the target line, which was presented on an oscilloscope and automatically moved, with the line which represented their own force generated by grip movement with the left hand. Tracking speed (experiment 1) and tracking predictability (experiment 2) were manipulated to vary task difficulty. N140, P300, and reaction time (RT) in the oddball task and tracking accuracy in the tracking task were measured. RESULTS: The P300 and N140 amplitudes were reduced in the dual-task condition compared to those in the oddball-only condition. The fastest tracking speed produced lower tracking accuracy and later RT. However, the tracking speed did not affect the P300 or N140 amplitudes. In contrast, the P300 amplitude was smaller when the change in tracking direction was unpredictable than when it was predictable, without any differences in tracking accuracy or RT, N140. CONCLUSIONS: The differences in behaviors among N140, P300, and RT following manipulation of task difficulty support the multiple-resource hypothesis, which defines functionally separate pools of resources. SIGNIFICANCE: The present study may show that the P300 amplitude reflects modality-unspecific resource at more central level, and that the N140 amplitude involves perceptual resource.

Differential modulation of the short- and long-latency somatosensory evoked potentials in a forewarned reaction time task.

OBJECTIVE: We investigated modulation of the short- and long-latency somatosensory evoked potentials (SEPs) in a forewarned reaction time task. METHODS: A pair of warning (auditory) and imperative stimuli (somatosensory) was presented with a 2 s interstimulus interval. In movement condition, subjects responded by grip movement with the ipsilateral hand to the somatosensory stimulation when the imperative stimulus was presented. In counting condition, they silently counted the number of imperative stimuli. The SEPs in response to the imperative stimuli were recorded. RESULTS: Frontal N30 and central N60 amplitudes were significantly smaller in the movement than in the counting or rest conditions. None of the short-latency components differed between the counting and rest conditions. In contrast to the short-latency components, P80 was significantly larger in the counting than in the rest condition, and showed a further increase from the counting to the movement condition. The N140 amplitude was significantly larger in the movement than the rest condition, but was not changed between the counting and the rest conditions. CONCLUSIONS: The attenuation of the frontal N30 and central N60, and the enhancement of the P80 and possibly the N140 resulted from the centrifugal mechanism. The present findings may show the different effects of voluntary movement on the early and subsequent cortical processing of the relevant somatosensory information requiring a behavioral response. SIGNIFICANCE: The present study demonstrated the differential modulation of short- and long-latency components of SEPs in a forewarned reaction time task.

Differential influences of exercise intensity on information processing in the central nervous system.

The influence of exercise intensity on information processing in the central nervous system was investigated using P300 and no-go P300 event-related potentials. Twelve subjects (22-33 years) performed a go/no-go reaction time task in a control condition, and again after high-, medium-, and low-intensity pedaling exercises. Compared to the control condition, P300 amplitude decreased after high-intensity pedaling exercise and increased after medium-intensity pedaling exercise. There was no change after low-intensity pedaling exercise. These results suggested that the amount of attentional resources devoted to a given task decreased after high-intensity exercise and increased after medium-intensity exercise. The findings also suggest that changes in P300 amplitude are an inverted U-shaped behavior of differences in exercise intensity. In addition, no-go P300 amplitude showed the same changes as P300 amplitude at different exercise intensities. This indicates that differences in exercise intensity influenced not only the intensity of processing the requirement for a go response, but also processing of the need for a no-go response. It is concluded that differences in exercise intensity influenced information processing in the CNS.

Passive enhancement of the somatosensory P100 and N140 in an active attention task using deviant alone condition.

OBJECTIVE: We investigated the changes in the somatosensory P100 and N140 during passive (reading) versus active tasks (counting, button pressing) and oddball (target=20%, standard=80%) versus deviant alone conditions (standards were omitted). METHODS: Nine healthy subjects performed the 3 tasks (reading, counting and button pressing) under two conditions. Standard and target electrical stimuli were presented in a random order to the index or middle fingers of the left hand at a constant 800 ms interstimulus interval in the oddball conditions. In the deviant alone conditions, only target stimuli were presented with the same timing as in the oddball conditions. RESULTS: The N140 amplitude increased for the deviant alone stimuli compared with the oddball standard and target stimuli regardless of whether the task was passive or active, indicating passive shifts of attention related to temporal infrequency. The P100 amplitude also increased for the deviant alone stimuli compared with the oddball standard and target stimuli in both passive and active tasks, but the enhancement seemed to be even smaller than that of the N140 amplitude. CONCLUSIONS: The somatosensory N140 passively increased even if subjects tried to attend actively to the stimulus source when the deviant alone condition was used. This change in N140 amplitude may be related to a strong orienting effect against a 'silent' background. SIGNIFICANCE: The present study provided evidence that the N140 is an indicator of passive attention against a silent background when the deviant alone condition or long interstimulus interval was used.

Differential modulation of temporal and frontal components of the somatosensory N140 and the effect of interstimulus interval in a selective attention task.

The modulation of the somatosensory N140 was examined in a selective attention task where a control condition was applied and the interstimulus interval (ISI) was varied. Electrical stimuli were randomly presented to the left index (p=0.4) and middle fingers (p=0.1), and right index (p=0.4) and middle fingers (p=0.1). In the attend-right condition, subjects were instructed to count silently the number of infrequent target stimuli presented to the right middle finger, and to the left middle finger in the attend-left condition. They had no task in the control condition. Each condition was performed with two different sets of ISI (mean 400 vs. 800 ms). The somatosensory N140 elicited by frequent standard stimuli was analyzed. The N140 amplitude was larger for the attended ERP compared to the control and unattended ERPs. This attention effect was more marked at the frontal electrodes compared to the temporal electrodes contralateral to the stimulation side. Furthermore, the attention effect at the frontal electrode was larger when the ISI was 800 ms than when it was 400 ms. The N140 amplitude did not differ between the control and unattended ERPs, which might show that a small processing negativity (PN) occurred during the control condition or difference in vigilance level between them. In conclusion, the early lateral ("temporal") and late midline ("frontal") components of the N1 (N140) show different behavior, and thus may have different functional significance. Enhancement of the attention effect at the frontal electrode in the longer ISI condition supports the hypothesis that it is related to stronger, voluntary maintenance of the attentional trace.

Effects of a go/nogo task on event-related potentials following somatosensory stimulation.

OBJECTIVE: We investigated the effects of a go/nogo task on event-related potentials (ERPs) evoked by somatosensory stimuli. METHODS: ERPs following electrical stimulation of the second (go stimulus) or fifth (nogo stimulus) left-handed digit were recorded from 9 subjects. The recordings were conducted in 3 conditions: Control, Count and Movement. The subjects were instructed to count the go stimuli silently in Count, and respond to the go stimuli by grasping right hands in Movement. Go and nogo stimuli were presented at an even probability. RESULTS: N140 was recorded in all conditions and P300 in Count and Movement. The mean amplitudes of the nogo stimuli in the interval 140-200 msec and nogo-N140 amplitude were significantly more negative than those of the go stimuli in Count or Movement. Nogo-P300 was larger in amplitude than go-P300 in Movement but not Count. The effect of P300 was applied to Fz and Cz, but not at Pz. CONCLUSIONS: In the present study, effects of a somatosensory go/nogo task on ERPs were investigated, and our findings were very similar to those of previous studies using visual and auditory go/nogo tasks. Therefore, we suggest that cortical activities relating to go/nogo tasks are not dependent on sensory modalities. SIGNIFICANCE: The present study showed for the first time the go/nogo effects on somatosensory-evoked ERPs. These effects were similar to those in visual and auditory ERP studies.

Gating of somatosensory evoked magnetic fields during the preparatory period of self-initiated finger movement.

The temporal change in somatosensory evoked magnetic fields (SEFs) in the preparatory period of self-initiated voluntary movement was investigated. The SEF following stimulation of the right median nerve was recorded, using a 204-channel whole-head MEG system, in nine healthy subjects during a self-initiated extension of the right index finger every 5 to 7 s. The preparatory period before finger movement was divided into six subperiods, and the MEG signals following the stimulation in each subperiod were averaged separately. SEFs were also recorded in the resting state. The ECD strengths for N20m and P60m were not significantly changed in any subperiod before movement compared with those in the resting state. The ECD strength for P30m was significantly smaller 500 ms or less before movement than during the resting state and 1,500 ms or less before movement compared to that during the period from 3,000 to 4,000 ms before movement. Thus, we confirmed that the SEF components were attenuated even during a period of self-initiated voluntary movement. The modulation started at least 1,500 ms before movement and was greater for the P30m than the N20m component. These findings suggested that motor-associated cortices attenuated SEF components by a centrifugal gating process.

Mechanisms of differences in gating effects on short-and long-latency somatosensory evoked potentials relating to movement.

We investigated the mechanisms underlying the differences in gating effects on short- and long-latency somatosensory evoked potentials (SEPs) relating to movement. SEPs were recorded in normal subjects for 6 different tasks in Experiment 1: Control, Movement, Distraction, Attention, Movement during Distraction and Movement during Attention, and for 4 different tasks in Experiment 2: Control, Passive Movement, Contralateral Movement and Movement Imagery. The amplitudes of short-latency SEPs were significantly reduced by active and passive movement of the stimulated hand, but long-latency SEPs (N140-P200) were significantly enhanced by active movement of the stimulated hand. Attention, Distraction, Contralateral Movement and Movement Imagery did not affect the amplitudes of SEPs. The degree of enhancement of long-latency SEPs by active Movement was greater than that by active movement with Attention or Distraction. Gating effects on long-latency SEPs were different from those on short-latency SEPs. Since this effect was not related to Attention/Distraction, Passive Movement, Movement Imagery or Movement of another site, it is probably due to specific centrifugal effects, which are different from more direct gating effects on short-latency components. This study showed the difference in gating effects on somatosensory perception depending on time periods following stimulation, which may indicate an interaction between motor and somatosensory cortex.

Somatosensory N250 and P300 during discrimination tasks.

We investigated the event-related potentials (N250 and P300) during three kinds of somatosensory discrimination tasks (oddball task). Strong (standard: 90%) and weak (deviant: 10%) electrical stimuli were randomly delivered to the right median nerve at the wrist with a 500-ms constant interstimulus interval. In a passive situation, subjects read a self-selected book, ignoring all stimuli (ignore condition). One of the active situations was a mental counting task (count condition), and another required pressing a button to deviant stimuli as quickly as possible (motor response condition). The N250-P300 complex was elicited by deviant stimuli in the active-attended situations, but not found in the ignore condition. The N250 peak amplitude was unchanged between the count and motor response conditions whereas P300 changed. In addition, the N250 latency significantly correlated with the reaction time, but the P300 latency did not. These results indicate that the somatosensory N250 reflects an attentive process which is related to the temporal aspect of behavioral response.

Changes in the somatosensory N250 and P300 by the variation of reaction time.

We investigated the relationship between somatosensory event-related potentials (ERP) and the variation of reaction time (RT). For this purpose, we recorded the ERPs (N250 and P300) in fast- and slow-reaction trials during a somatosensory discrimination task. Strong, standard, and weak target electrical stimuli were randomly delivered to the left median nerve at the wrist with a random interstimulus interval (900-1,100 ms). All the subjects were instructed to respond by pressing a button with their right thumb as fast as possible whenever a target stimulus was presented. We divided all the trials into fast- and slow-RT trials and averaged the data. N250 latency tended to be delayed when the RT was slow, but not significantly. P300 latency was delayed significantly when the RT was slow, but to a much lesser extent than the RT delay, so we concluded that the change of RT was not fully determined by the processes reflected by the somatosensory N250 or P300. Furthermore, the larger and earlier P300 in the fast-RT trials implied that when larger amounts of attentional resources were allocated to a given task, the speed of stimulus evaluation somewhat increased and RT was shortened to a great extent. N250 amplitude did not significantly vary in the two RT clusters. In conclusion, the somatosensory N250 reflects active target detection, which is relatively independent of the modulation of the response speed, whereas the somatosensory P300 could change without manipulation of either the stimulus or the response processing demand.