Inhibition of pericranial muscle activity, respiration, and heart rate enhances auditory sensitivity

We investigated whether previously observed inhibition of pericranial electromyographic (EMG) activity, respiration, and heart rate during sensory intake processes improves auditory sensitivity. Participants had to detect weak auditory stimuli. We found that EMG activity in masticatory and lower facial muscles, respiration, and heart rate were more strongly inhibited when stimulus intensity was gradually lowered to threshold level whereas EMG of upper facial muscles progressively increased. Detection of near-threshold stimuli was inversely related to prestimulus EMG levels in masticatory and lower facial muscles. In two additional experiments, it was investigated whether steady, voluntary contractions negatively influence auditory sensitivity. As expected, contraction of zygomaticus produced an increase in auditory threshold in comparison with contraction of corrugator or first dorsal interosseus. It is concluded that attention to external stimuli is accompanied by quieting of those somatic activities that produce internal noise or are accompanied by impaired middle ear transmission of auditory stimuli.     

Pericranial muscular,respiratory, and heart rate components of the orienting response

We have earlier found that voluntary attention to weak auditory stimuli induces inhibition of respiration, heart rate, and electromyographic (EMG) activity of masticatory and lower facial muscles and that these responses lower the auditory threshold for low-frequency sounds. In the current study, we examined whether this inhibitory response pattern also occurs during involuntary orienting to novel, nonsignal sounds. Environmental sounds of low intensity were presented unexpectedly during the performance of a reading task. Orienting responses (ORs) were elicited as indicated by heart rate deceleration and skin conductance responses. Inhibitory respiratory and pericranial EMG responses appeared to be intrinsic components of the OR. Together with the autonomic responses, they habituated when a nonsignal auditory stimulus was repeatedly presented. Our results also suggest that eye and pinna movements occurred toward the sound source. The results of the current study are consistent with the hypothesis of Sokolov (1963) that the primary function of the OR is enhancement of sensory sensitivity.     

Facial EMG and heart rate responses to emotion-inducing film clips in boys with disruptive behavior disorders

We examined aspects of emotional empathy across different physiological response systems in boys with disruptive behavior disorders (DBD) and normal controls. Heart rate (HR) and electromyographic (EMG) reactivity in zygomaticus major and corrugator supercilii muscles were monitored during sadness-, anger-, or happiness-inducing film clips. Relative to controls, DBD boys showed significantly less HR reduction during sadness, and a smaller increase in corrugator EMG activity both during sadness and anger. No significant group differences emerged in HR and zygomaticus EMG responsivity during happiness. We also examined cardiac activity at rest and found higher resting HR and lower respiratory sinus arrhythmia in DBD boys compared to controls. Findings give evidence for a selective impairment in empathy with sadness and anger (not happiness) among DBD boys who exhibit relatively high levels of anxiety and poor emotional control.     

Reduced intracortical inhibition during the foreperiod of a warned reaction time task

Reaction time (RT) is shortened when the response signal is preceded by a warning signal, a finding that has been attributed to response preparation during the foreperiod between the warning and response signals. Research suggests an increased excitability of cortical movement representations associated with response preparation during the foreperiod of a warned RT task (Davranche et al. in Eur J Neurosci 25:3766–3774, 2007). However when the foreperiod duration is short and constant, the motor evoked potential (MEP) amplitude elicited by transcranial magnetic stimulation (TMS) during the foreperiod is suppressed (Touge et al. in Clin Neurophysiol 111:1216–1226, 1998), suggesting a competing inhibitory process. Three experiments measured MEP amplitude and intracortical inhibition during the foreperiod of a warned RT task in which the response was a flexion of the right index finger. Experiments 1 and 2 measured short-interval intracortical inhibition (SICI) with paired TMS pulses separated by inter-stimulus intervals (ISIs) of 3 (SICI₃) and 1.5 ms (SICI_1.5), respectively. Experiment 3 measured long-interval intracortical inhibition (LICI) with paired TMS pulses with an ISI of 100 ms (LICI₁₀₀). In all experiments MEP amplitude was smaller in the warned condition than in the unwarned condition. There was less SICI₃ in the warned condition than in the unwarned condition (Experiment 1) whereas SICI_1.5 was similar in both conditions (Experiment 2). There was less LICI₁₀₀ in the warned condition than in the unwarned condition (Experiment 3). The intracortical inhibitory processes measured here cannot explain the suppression of MEP amplitude in the warned condition. We propose that the suppression of MEP amplitude is the result of an inhibitory mechanism, which acts on primary motor cortex to prevent premature response during the foreperiod.     

The cardiac cycle time effect revisited: temporal dynamics of the central-vagal modulation of heart rate in human reaction time tasks

Lacey and Lacey (1974) suggested that during reaction time tasks higher brain centers dynamically adjust efferent vagal nerve pulses to the sino-atrial node of the heart, inducing phase-dependent heart rate changes. Since then, animal and human neuro-physiological results have provided evidence for this hypothesis. Higher subcortical and cortical brain centers may have reciprocal interactive pathways relating to autonomic control comparable to those at the level of peripheral autonomic changes and brain stem reflexes. In humans such central effects may be observed in the short latency vagal control of heart rate that has been studied mostly in reaction time (RT) tasks. RT task parameters modulate vagal pulses to the cardiac sino-atrial node (SAN), which in turn exerts a phase-dependent change in the ongoing cardiac interbeat interval. Simulations of human RT task effects in an animal model of heart rate change support this hypothesis. The current study examined evidence for vagal control of three human phasic heart rate responses in RT tasks. The evidence indicates that the initiation of an RT response triggers a reflexive shift from vagal activation to vagal inhibition. This shift is cardiac cycle phase dependent. Graded anticipatory cardiac deceleration during the warning interval of an RT task varies with task relevance and time uncertainty. This response may be part of a control process engaged in time keeping. Hence, temporal variables mediate the central-autonomic-vagal modulation of heart rate.     

Inter-relationships among anticipatory EMG activity,Hoffmann reflex amplitude and EMG reaction time during voluntary standing movement

Summary In order to understand the process of executing a voluntary standing movement, the parameters latency (AEA-LT), duration (AEA-DUR) and amplitude (AEA-AMP) of the anticipatory electromyographic (EMG) activity (AEA) in the tibialis anterior muscle, Hoffmann (H) reflex amplitude in the soleus muscle (Sol) prior to the onset of EMG activity in that muscle, and EMG reaction time (EMG-RT) were measured during heel raising from the standing position. The following results were obtained: the three parameters of AEA correlated with EMG-RT in each subject; the average values for all nine normal subjects werer=0.856 for AEA-DUR,r=0.448 for AEA-LT andr= –0.215 for AEA-AMP; for the group the mean value of AEA-DUR correlated significantly with that of EMG-RT (r=0.983,P<0.01), while no such significant correlation was observed for AEA-LT; the average value of the AEA-DUR in three slower EMG-RT performers (SLOW-PFM) was significantly longer (P<0.05) than that in three faster ones (FAST-PFM), while no significant difference in the AEA-LT was observed; and lastly the total area of the anticipatory suppression of the Sol H reflex amplitude in the SLOW-PFM was greater than that in the FAST-PFM. These results suggest that AEA-DUR, representing postural responses, rather than AEA-LT, reflecting cognitive processes, may have had a close link with EMG-RT, and that the increased suppression in Sol H reflex amplitude originated from the increased anticipatory postural requirement, thus bringing about the EMG-RT delay.     

Amplitude and bilateral coherency of facial and jaw-elevator EMG activity as an index of effort during a two-choice serial reaction task

In earlier studies, positive but inconsistent relationships have been reported between mental effort and electro-myogram (EMG) amplitude in task-irrelevant limb muscles. In this study, we explored whether facial EMG activity would provide more consistent results. Tonic EMG activity of six different facial and jaw-elevator muscles was bilaterally recorded during a two-choice serial reaction task with paced presentation of auditory or visual signals. In Experiment 1, task load (signal presentation rate) was kept constant for 20 min at the level of the subject's maximal capacity. In Experiment 2, task load was increased in a stepwise fashion over six successive 2-min periods from sub- to supramaximal capacity levels. EMG amplitude and coherency between momentary bilateral amplitude fluctuations were measured. In Experiment 1, EMG amplitude of frontalis, corrugator supercilii, and orbicularis oris inferior showed a strong gradual increase throughout the task period, whereas task performance remained fairly stable. Orbicularis oculi, zygomaticus major, and temporalis EMG showed a much smaller increase or no increase. In Experiment 2, the first three muscles showed a fairly consistent increase in EMG amplitude with increasing task load. Orbicularis oculi and zygomaticus major were not active until task load became supramaximal. Effects of stimulus modality or laterality were not found in any experiment. These results are consistent with the notion that EMG amplitude of frontalis, corrugator, and orbicularis oris provides a sensitive index of the degree of exerted mental effort.     

Loads applied tangential to a fingertip during an object restraint task can trigger short-latency as well as long-latency EMG responses in hand muscles

Electrical stimulation of the digital nerves can cause short- and long-latency increases in electromyographic activity (EMG) of the hand muscles, but mechanical stimulation of primarily tactile afferents in the digits generally evokes only a long-latency increase in EMG. To examine whether such stimuli can elicit short-latency reflex responses, we recorded EMG over the first dorsal interosseous muscle when subjects (n=13) used the tip of the right index finger to restrain a horizontally oriented plate from moving when very brisk tangential forces were applied in the distal direction. The plate was subjected to ramp-and-hold pulling loads at two intensities (a 1-N load applied at 32 N/s or a 2-N load applied at 64 N/s) at times unpredictable to the subjects (mean interval 2 s; trial duration 500 ms). The contact surface of the manipulandum was covered with rayon—a slippery material. For each load, EMG was averaged for 128 consecutive trials with reference to the ramp onset. In all subjects, an automatic increase in grip force was triggered by the loads applied at 32 N/s; the mean onset latency of the EMG response was 59.8±0.9 (mean ± SE) ms. In seven subjects (54%) this long-latency response was preceded by a weak short-latency excitation at 34.6±2.9 ms. With the loads applied at 64 N/s, the long-latency response occurred slightly earlier (58.9±1.7 ms) and, with one exception, all subjects generated a short-latency EMG response (34.9±1.3 ms). Despite the higher background grip force that subjects adopted during the stronger loads (4.9±0.3 N vs 2.5±0.2 N), the incidence of slips was higher—the manipulandum escaped from the grasp in 37±5% of trials with the 64 N/s ramps, but in only 18±4% with the 32-N/s ramps. The deformation of the fingertip caused by the tangential load, rather than incipient or overt slips, triggered the short-latency responses because such responses occurred even when the finger pad was fixed to the manipulandum with double-sided adhesive tape so that no slips occurred.     

Resting cardiac vagal tone predicts intraindividual reaction time variability during an attention task in a sample of young and healthy adults

Intraindividual reaction time variability (IIV), defined as the variability in trial‐to‐trial response times, is thought to serve as an index of central nervous system function. As such, greater IIV reflects both poorer executive brain function and cognitive control, in addition to lapses in attention. Resting‐state vagally mediated heart rate variability (vmHRV), a psychophysiological index of self‐regulatory abilities, has been linked with executive brain function and cognitive control such that those with greater resting‐state vmHRV often perform better on cognitive tasks. However, research has yet to investigate the direct relationship between resting vmHRV and task IIV. The present study sought to examine this relationship in a sample of 104 young and healthy participants who first completed a 5‐min resting‐baseline period during which resting‐state vmHRV was assessed. Participants then completed an attentional (target detection) task, where reaction time, accuracy, and trial‐to‐trial IIV were obtained. Results showed resting vmHRV to be significantly related to IIV, such that lower resting vmHRV predicted higher IIV on the task, even when controlling for several covariates (including mean reaction time and accuracy). Overall, our results provide further evidence for the link between resting vmHRV and cognitive control, and extend these notions to the domain of lapses in attention, as indexed by IIV. Implications and recommendations for future research on resting vmHRV and cognition are discussed.     

Reaction time and spinal excitability in a simple reaction time task

H and Tendon reflexes were elicited from subjects at varying intervals after the reaction signal (RS) of a simple reaction time (RT) task when the response involved a rapid plantar flexion of the left foot. It was found that a reflex stimulus presented in close temporal proximity to the RS significantly shortened RT in comparison with the RT when no reflex stimulus was presented. This effect was discussed in terms of the intersensory facilitation of RT. No significant evidence was found in support of previous evidence that RT is delayed when a reflex stimulus occurs about 100 msec after the RS. A large facilitation of reflex amplitude was observed commencing 90–120 msec before the onset of the voluntary movement. This was discussed in terms of the hypothesised stages of information processing involved in the latent period of simple RT.     

Phasic heart rate changes during word translation of different difficulties

The heart rate (HR) can be modulated by diverse mental activities ranging from stimulus anticipation to higher order cognitive information processing. In the present study we report on HR changes during word translation and examine how the HR is influenced by the difficulty of the translation task. Twelve students of translation and interpreting were presented English high- and low-frequency words as well as familiar and unfamiliar technical terms that had to be translated into German. Analyses revealed that words of higher translation difficulty were accompanied by a more pronounced HR deceleration than words that were easier to translate. We additionally show that anticipatory HR deceleration and HR changes induced by motor preparation and activity due to typing the translation do not depend on task difficulty. These results provide first evidence of a link between task difficulty in language translation and event-related HR changes.     

Reaction time changes with the hazard rate for a behaviorally relevant event when monkeys perform a delayed wrist movement task

Anticipating the timing of behaviorally relevant events is crucial for organizing movement. The time to initiate actions based on events (i.e., reaction time (RT)) is a useful measure to quantify states of anticipation. Few studies have examined how anticipation affects the timing of limb movements. We addressed this question behaviorally with two macaque monkeys performing delayed wrist movement tasks. The interval between target onset and go signal (i.e., foreperiod) varied randomly from 1 to 2 s. The probability that the go signal was about to occur (i.e., hazard rate) increased as the foreperiod increased. The kinematics of wrist movements was not influenced by foreperiod duration. Analyzing RT data with the LATER model indicated that RT distributions swiveled on reciprobit plots as foreperiods increased, suggesting that changes in RT distributions were due to changes in anticipation. RT was inversely related to hazard rate. To better understand the general implications of anticipatory states, we introduced an additional rectangular foreperiod distribution that ranged from 0.9 to 1.5 s. For that distribution, the hazard rate peaks were higher than those of the 1-2 s distribution. Changes in RT were clearly explained by quantitative differences in hazard rate. The decrease in RT in the 0.9-1.5 s foreperiod distribution was greater than that in the 1-2 s foreperiod. Thus, monkeys learned the temporal structure of foreperiod distributions and anticipated the onset of the go signal, based on hazard rates.     

Relationships between the type A behavior pattern and phasic heart rate responses during a reaction time task

Type A and B college students performed a signalled reaction time task with a 17-s fixed preparatory internal (PI) while heart rate was recorded. The analysis of the first half of the PI indicated a triphasic heart rate response (deceleration-acceleration-deceleration) to the warning signal, followed by a return toward baseline. No group differences were found. During the latter half of the PI, the Type B subjects exhibited a time-locked heart rate deceleration which reached its maximum at the second immediately prior to the onset of the imperative stimulus. The Type A subjects exhibited maximum deceleration earlier in the PI. These findings are consistent with previous work indicating that Type A's have difficulty maintaining their attention over relatively long PI's of reaction time tasks.     

Relationship between systolic time intervals and heart rate during four circulatory stress tests

Summary The linear regression equations between heart rate and systolic time intervals were calculated before and during a handgrip test, an orthostatic test, the Valsalva test and a cold pressor test. The subjects were 30 healthy men, average age 20 years. During the 1st min of orthostasis the regression line of the left ventricular ejection time (LVET) was significantly (P<0.05) steeper than at rest and that of the pre-ejection period (PEP) was significantly (P<0.01) less steep than at rest, and the regression between HR and the PEP/LVET ratio deviated significantly (P<0.001) from zero. During the Valsalva maneuver, the regression line of the LVET became significantly (P<0.001) steeper than at rest and the regression coefficient of the PEP changed from negative to positive, the difference being significant (P<0.001); the regression between HR and the PEP/LVET also deviated significantly (P<0.001) from zero. During the cold pressor test the regression line of the electromechanic systole (Q-S2 time) was significantly (P<0.01) less steep than at rest. It was concluded that the use of regression equations calculated for the systolic time intervals and heart rate at rest can lead to errors when applied to rate correction of systolic time intervals during an orthostatic, Valsalva, or a cold pressor test.     

Excitatory and inhibitory processes in primary motor cortex during the foreperiod of a warned reaction time task are unrelated to response expectancy

Reaction time (RT) is shortened when a warning signal precedes the response signal, a finding attributed to response preparation during the foreperiod between the warning and response signals. In a previous experiment, we delivered transcranial magnetic stimulation (TMS) during the short constant foreperiod of a warned RT task and found simultaneous suppression of motor evoked potential (MEP) amplitude and reduction of short-interval intracortical inhibition (SICI) on warned trials (Sinclair and Hammond in Exp Brain Res 186:385–392, 2008). To investigate the extent to which these phenomena are associated with response preparation we measured MEP amplitude and SICI during the foreperiod of a warned RT task in which three different warning signals specified the probability (0, 0.5, or 0.83) of response signal presentation. MEP amplitude was suppressed (Experiment 1) and SICI reduced (Experiment 2) equally in all of the warned conditions relative to when TMS was delivered in the inter-trial interval (ITI) suggesting that the modulation of primary motor cortex excitability during the foreperiod does not depend on momentary response expectancy induced by the warning signal. The reduction of SICI and suppression of MEP amplitude can be explained by assuming that a warning signal induces automatic motor cortical activation which is balanced by a competing inhibition to prevent premature response. A composite measure which weighted both speed and accuracy of response was positively correlated with the MEP amplitude during both the foreperiod and the ITI, suggesting that high motor cortical excitability is associated with optimized preparatory strategies for fast and accurate response.     

Emotional modulation of skin conductance and eyeblink responses to a startle probe

In this study, I examined emotional modulation of the eyeblink, skin conductance, and cardiac responses to an acoustic startle (103 dB[A] white noise) probe. Twenty-five female and 17 male undergraduates imagined pleasant, neutral, and fearful situations in a tone-cued imagery procedure. Both the eyeblink and skin conductance responses to startle probes were potentiated (larger magnitude, shorter latency) during fear as compared with neutral and pleasant imagery. The amount of emotional modulation in these two response systems was significantly correlated both between and within subjects. The startle probe interrupted ongoing cardiac deceleration during the imagery task, but this interruption was not related to the emotional content of imagery.     

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     

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.     

Activity of ventrolateral thalamic neurons in relation to a simple reaction time task in the cat

Unrestrained cats performed ballistic forelimb flexion movements triggered by an auditory stimulus (CS) on a simple reaction time (RT) paradigm. During the variable foreperiod the subject was required to hold down a lever and to release it on presentation of the CS. The RTs ranged from 200 to 300 ms. The activity of single neurons of the ventrolateral nucleus of the thalamus (VL) was recorded bilaterally. More than 40% of the 166 units recorded in the VL contralateral to the performing limb presented, after the CS, changes of activity with a latency less than 100 ms and were classified into three types: (1) Twenty-five units had a short latency transient increase of activity 10 to 30 ms after the CS, followed by a longer increase or decrease in activity. Short latency increase as well as subsequent increase of the firing rate were not correlated to the RTs. (2) Twenty-nine units showed a 40-60 ms latency increase of activity which lasted long enough to continue during the forelimb movement. These units displayed a correlation between the RTs and the mean firing rate measured in the 40-100 ms period after the CS. The more the cells were activated, the shorter the RTs. (3) Fifteen units presented a reciprocal pattern of discharge with respect to the type (2) units. The firing rate decreased with latencies ranging from 20 to 90 ms after the CS. Only 14,5% of the 96 units recorded in the VL ipsilateral to the performing limb presented changes of activity starting in the 100 ms period following the CS. Background firing levels as well as phasic activity were rather low compared to those observed contralaterally. Sixteen units showed burst activity while the cat was performing but burst pattern was not time-related to the task. In an unconditioned animal, a very low level of activity and an absence of modulations were observed in both VLs.     

Excess heart rate and systolic blood pressure during psychological stress in relation to metabolic demand in adolescents

Cardiovascular responses during exercise are matched to the increased metabolic demand, but this may not be the case during psychological stress. No studies to date have tested this hypothesis in youth. Fifty-four youth, ages 13-16 years completed two visits. Heart rate (HR), systolic blood pressure (SBP), and oxygen (O(2)) consumption were measured during a graded exercise test on one day and during psychological stress reactivity (star tracing, speech) on another day. Predicted HR and SBP values during psychological stress were calculated based on HR-O(2) and SBP-O(2) relationships calculated during graded exercise. At a given O(2) consumption, actual HR was greater (p<0.02) than predicted for all stress tasks. Actual SBP was greater (p<0.001) than predicted for all stress tasks. This was the first study to demonstrate that cardiovascular responses were in excess of what would be expected based on metabolic demand in youth.