P79-T Sensory-motor integration during a visuomotor sequence learning task

The effect of sensory signals coming from skin and muscle afferents on the sensorimotor cortical networks is entitled as sensory-motor integration (SMI). SMI can be studied electrophysiologically by the motor cortex excitability changes in response to peripheral sensory stimulation. These changes include the periods of short afferent inhibition (SAI), afferent facilitation (AF), and late afferent inhibition (LAI). During the early period of motor skill acquisition, motor cortex excitability increases and changes occur in the area covered by the relevant zone of the motor cortex. In the late period, these give place to the morphological changes, such as synaptogenesis. SAI decreases during learning the motor skills, while LAI increases during motor activity. In this review, the role of SMI in the process of motor learning and transcranial magnetic stimulation techniques performed for studying SMI is summarized.

In this experiment, which was concerned with reaction times to regularly recurring visual stimuli, four experienced Ss made 21 serial responses at eight interstimulus intervals with eight replications each. The experiment was designed to provide answers to the following questions. With regularly recurring visual stimuli, (a) what is the relationship between foreperiod length and mean reaction time to light at the asymptote of the reaction time practice curve, and (b) what are the differences, for various foreperiod lengths, in the effects of practice on mean reaction time to light? The predicted answers to both questions (a) and (b) were confirmed. First, the relationship between interstimulus time interval and reaction time to regularly recurring visual stimuli is best depicted as an increasing function which reaches an asymptote at a different time interval for each S. In addition, practice results in a greater decrease in reaction time for the 1- and 2-sec. interstimulus intervals, and especially for the former, than for longer intervals; this effect is most pronounced after one experience with the given interstimulus interval.

Frequent object dropping in carpal tunnel syndrome: a consequence of impaired sensorimotor integration?

The present study evaluated the use of slow rates of stimulus presentation on the accuracy of the N1-P2 cortical response in estimating hearing threshold. Long interstimulus intervals (ISI) allow the non-specific component of the N1 response to emerge, believed to reflect widespread cortical arousal that facilitates sensory and motor responses. We examined whether the non-specific N1 would be elicited at intensity levels near threshold. Event-related potentials were recorded to 0.5-, 1.0, and 4.0-kHz tone bursts with a long ISI (8–12 s) while the eleven subjects read a book. The stimulus level varied from -5 to 45 dB nHL. The 1.0-kHz tone burst was also presented with a shorter ISI (1.5–2.5 s), akin to that typically used in the audiological setting. The amplitude of N1-P2 was significantly enhanced in the long compared to short ISI condition, but, importantly, only for the stimuli with a level ≥25 dB nHL. Therefore, the N1-P2 recorded with long ISIs was not more precise in estimating threshold than that recorded with short ISIs, remaining visible to within 10 dB of behavioural threshold.

Background:The combination of motor imagery (MI) and afferent input with electricalstimulation (ES) enhances the excitability of the corticospinal tractcompared with motor imagery alone or electrical stimulation alone. However,its therapeutic effect is unknown in patients with hemiparetic stroke. Weperformed a preliminary examination of the therapeutic effects of MI + ES onupper extremity (UE) motor function in patients with chronic stroke.Methods:A total of 10 patients with chronic stroke demonstrating severe hemiparesisparticipated. The imagined task was extension of the affected finger.Peripheral nerve electrical stimulation was applied to the radial nerve atthe spiral groove. MI + ES intervention was conducted for 10 days. UE motorfunction as assessed with the Fugl–Meyer assessment UE motor score (FMA-UE),the amount of the affected UE use in daily life as assessed with a MotorActivity Log (MAL-AOU), and the degree of hypertonia in flexor muscles asassessed with the Modified Ashworth Scale (MAS) were evaluated before andafter intervention. To assess the change in spinal neural circuits,reciprocal inhibition between forearm extensor and flexor muscles with the Hreflex conditioning-test paradigm at interstimulus intervals (ISIs) of 0,20, and 100 ms were measured before and after intervention.Results:UE motor function, the amount of the affected UE use, and muscle hypertoniain flexor muscles were significantly improved after MI + ES intervention(FMA-UE: p < 0.01, MAL-AOU: p <0.01, MAS: p = 0.02). Neurophysiologically, theintervention induced restoration of reciprocal inhibition from the forearmextensor to the flexor muscles (ISI at 0 ms: p = 0.03, ISIat 20 ms: p = 0.03, ISI at 100 ms: p =0.01).Conclusion:MI + ES intervention was effective for improving UE motor function inpatients with severe paralysis.

Effect of spatial attention on human sensorimotor integration studied by transcranial magnetic stimulation

Evidence suggests that concussion prolongs reaction time (RT). We have developed a simple, reliable clinical tool for measuring reaction time that may be of value in the assessment of concussion in athletes. To compare baseline values of clinical RT (RT(clin)) obtained using the new clinical reaction time apparatus with computerized RT (RT(comp)) obtained using a validated computerized neuropsychological test battery. Cross-sectional study. Data were collected during a National Collegiate Athletic Association Division I collegiate football team's preparticipation physical examination session. Ninety-four Division I collegiate football players. The RT(clin) was measured using a 1.3-m measuring stick embedded in a weighted rubber disk that was released and caught as quickly as possible. The RT(comp) was measured using the simple RT component of CogState Sport. For the 68 athletes whose CogState Sport tests passed the program's integrity check, RT(clin) and RT(comp) were correlated (r = 0.445, P < .001). Overall, mean RT(clin) was shorter and less variable than mean RT(comp) (203 +/- 20 milliseconds versus 268 +/- 44 milliseconds; P < .001). When RT(clin) and RT(comp) were compared between those athletes with (n = 68) and those without (n = 26) valid CogState Sport test sessions, mean RT(clin) was similar (202 +/- 19 milliseconds versus 207 +/- 23 milliseconds; P = .390), but mean RT(comp) was different (258 +/- 35 milliseconds versus 290 +/- 55 milliseconds; P = .009). The RT(clin) was positively correlated with RT(comp) and yielded more consistent reaction time values during baseline testing. Given that RT(clin) is easy to measure using simple, inexpensive equipment, further prospective study is warranted to determine its clinical utility in the assessment of concussion in athletes.

Slow potential changes and choice reaction time as a function of interstimulus interval

This study investigated the effect of variable interstimulus intervals (ISIs) on behavioral reaction time (RT) and on the latency and amplitude of the auditory P300 using an auditory continuous performance task (ACPT) paradigm. Twenty subjects were instructed to respond to common stimuli and ignore a rare stimulus. Common stimuli were 1000-, 1500-, and 2000-Hz pure tones. The rare stimulus was a 250-Hz pure tone. ISIs of 1, 2, and 4 seconds were used for this investigation. A significant correlation between ISI, reaction time, P300 latency, correct rejections, and false alarm rates was found. A significant correlation between P300 latency, P300 amplitude, correct rejections, and false alarm rates was also observed. Likewise, a statistically significant increase in reaction time (RT) was observed as ISI increased. The ACPT paradigm in conjunction with the auditory P300 response can measure both behavioral and electrophysiologic changes that occur during active auditory attention and auditory cognitive processing tasks.

To investigate the role of repetitive peripheral magnetic stimulation (RPMS) on the postural component of motor performances, the long-lasting modulatory effect of RPMS on the stabilization of the elbow joint was examined in 13 healthy subjects. The resistance against very slow passive movements in the relaxed state was recorded simultaneously with the electromyogram (EMG) of the forearm extensor and flexor muscles. The experiments show that RPMS performed on the forearm flexor muscles increased the degree of stabilization of the elbow joint, whereas RPMS on the forearm extensor muscles caused a decrease in stabilization. This leads to the assumption that the postural component of motor tasks depends on the motor task itself: motor tasks like manipulation, pointing or grasping which are fine skilled movements require an increase in stabilization while goal-directed movements require a decrease in stabilization. Therefore RPMS is involved in sensorimotor integration and may modulate the motor program at the cortical level.

The present study explored the impact of the stimulus presentation rate on sequential effects in event-related potentials (ERPs) and reaction times (RTs). Random series of equiprobable tones were presented at interstimulus intervals (ISIs) of 1.3, 2.1, and 2.9 s. Fast and accurate choice responses to the tones were required. Although sequential effects in RTs were stable across all ISIs, the common first-order repetition effect in P300 amplitude was only observed at the 1.3-s ISI and not at the slower presentation rates. This dissociation between the first-order effects in RTs and ERPs speaks against an explanation of both effects by a common expectancy mechanism. In addition, sequential effects were observed as early as about 100 ms after stimulus onset in the lateralized readiness potential. Together with similar sequential effects in P300 latency, this finding supports a continuous flow model of information processing.

Transcranial magnetic stimulation (TMS) has allowed investigators to study intracortical inhibition and facilitation and sensorimotor integration in motor disorders and epilepsy. The authors used TMS to elucidate the pathophysiology of reflex myoclonus with giant somatosensory evoked potentials (SEP). The authors studied four patients with progressive myoclonic epilepsy. All patients had giant SEP elicited by mixed and digital nerve stimulation. They studied the response to paired-pulse TMS at interstimulus intervals (ISI) ranging from 1 to 15 ms and the conditioning effect of digital electrical stimulation at ISI ranging from 10 to 100 ms on the motor evoked potential amplitude to TMS. Digital stimulation markedly facilitated conditioned motor evoked potentials at ISI ranging from 25 to 40 ms in all patients. This pattern was significantly different from the inhibition observed in controls (n = 12) at the same ISI. In the patients, paired-pulse TMS showed a decrease in intracortical inhibition in the motor cortex in comparison with controls. These findings suggest cortical and subcortical components of abnormal sensorimotor integration in addition to hyperexcitability of the sensory and motor cortex in our myoclonic patients.

Reaction times (RTs) are typically slower and more variable in individuals with attention-deficit/hyperactivity disorder (ADHD). Analysis of the ex-Gaussian RT distribution, which is described by mu, sigma (mean and standard deviation, respectively, of the normal distribution) and tau (that of exponential distribution), reveals that individuals with ADHD do not display overall slower RTs but have a high proportion of extremely slow RTs, represented by a high tau value. Although this is a vital component for describing ADHD-related RT variability in school-aged children, adolescents, and adults, it has not been thoroughly studied at the preschool age. We assessed 65 preschoolers at risk of ADHD and 98 typically developing preschoolers with the Conners' Kiddie Continuous Performance Test (K-CPT) and parental and teacher reports of ADHD symptoms. We found that preschoolers at risk of ADHD had greater values for RT standard deviation, sigma, and tau than typically developing preschoolers at long inter-stimulus intervals (ISIs) (3s), but not at short ISIs (1.5s). This suggests that attention problems in preschool children may only be apparent in the tasks with a relatively slow event rate. Our study demonstrates that the ex-Gaussian tau value is essential for describing the inattentive component of task performance in preschoolers with heightened ADHD symptoms. Furthermore, the fact that the tau effect was modulated by ISI suggests that the longer duration (3s vs. 1.5s) is a non-optimal energetic state in preschoolers at risk of ADHD, and that this might account for the subtle attentional flaw in task performance.

Temporal integration of patterned stimuli was investigated by introducing an interstimulus interval (ISI) between brief exposures of two matrices of illuminated squares. These matrices were identical except for their spatial displacement, arranged such that they could be superimposed to yield either horizontal or vertical stripes. Choice reaction times to the composite stripe orientation were a progressively increasing function of ISI, suggesting some integration over an ISI range in excess of 224 msec. Similar functions were obtained with both regular and irregular order of ISI presentation. The results from an additional experiment employing an extraneous warning signal discounted the possibility that preparatory factors developing over the ISI were responsible for the obtained reaction time functions.

Suicide is a significant public health problem. Suicidal ideation (SI) increases the risk for completed suicide. However, the brain basis of SI is unknown. The objective of this study was to examine the neural correlates of self-monitoring in individuals at risk for suicide. We hypothesized that combat veterans with a history of SI relative to those without such a history would show altered activation in the anterior cingulate cortex and related circuitry during self-monitoring. Two groups of combat-exposed war veterans (13 men with and 13 men without history of SI) were studied. Both the SI and non-SI participants had two or more of the following: a) current major depressive disorder, b) current posttraumatic stress disorder, and c) history of mild traumatic brain injury, and each subject performed a validated stop task during functional magnetic resonance imaging. Error-related activation was compared between the SI and non-SI groups. The SI group demonstrated more error-related activation of the anterior cingulate (8256 mm(3), t = 2.51) and prefrontal cortex (i.e., clusters >2048 mm(3), voxelwise p < .05). The SI and non-SI participants showed similar behavioral task performance (i.e., mean error rate, F values < 0.63, p values > .43; and mean reaction times, F = 0.27, p = .61). These findings suggest neural correlates of altered self-monitoring in individuals with a history of SI and may further suggest that functional magnetic resonance imaging could be used to identify individuals at risk for suicide before they engage in suicidal behavior.