Changes In Stimulus Rate Research Articles

A novel method for estimating properties of attentional oscillators reveals an age-related decline in flexibility.

Dynamic attending theory proposes that the ability to track temporal cues in the auditory environment is governed by entrainment, the synchronization between internal oscillations and regularities in external auditory signals. Here, we focused on two key properties of internal oscillators: their preferred rate, the default rate in the absence of any input; and their flexibility, how they adapt to changes in rhythmic context. We developed methods to estimate oscillator properties (Experiment 1) and compared the estimates across tasks and individuals (Experiment 2). Preferred rates, estimated as the stimulus rates with peak performance, showed a harmonic relationship across measurements and were correlated with individuals' spontaneous motor tempo. Estimates from motor tasks were slower than those from the perceptual task, and the degree of slowing was consistent for each individual. Task performance decreased with trial-to-trial changes in stimulus rate, and responses on individual trials were biased toward the preceding trial's stimulus properties. Flexibility, quantified as an individual's ability to adapt to faster-than-previous rates, decreased with age. These findings show domain-specific rate preferences for the assumed oscillatory system underlying rhythm perception and production, and that this system loses its ability to flexibly adapt to changes in the external rhythmic context during aging.

Steady-state activation in somatosensory cortex after changes in stimulus rate during median nerve stimulation

Passive electrical stimulation activates various human somatosensory cortical systems including the contralateral primary somatosensory area (SI), bilateral secondary somatosensory area (SII) and bilateral insula. The effect of stimulation frequency on blood oxygenation level-dependent (BOLD) activity remains unclear. We acquired 3-T functional magnetic resonance imaging (fMRI) in eight healthy volunteers during electrical median nerve stimulation at frequencies of 1, 3 and 10 Hz. During stimulation BOLD signal changes showed activation in the contralateral SI, bilateral SII and bilateral insula. Results of fMRI analysis showed that these areas were progressively active with the increase of rate of stimulation. As a major finding, the contralateral SI showed an increase of peak of BOLD activation from 1 to 3 Hz but reached a plateau during 10-Hz stimulation. Our finding is of interest for basic research and for clinical applications in subjects unable to perform cognitive tasks in the fMRI scanner.

Steady State Activation in Primary Somatosensory Cortex after Changes in Stimulus Rate during Median Nerve Stimulation

Steady State Activation in Primary Somatosensory Cortex after Changes in Stimulus Rate during Median Nerve Stimulation

Brain-stem auditory evoked potentials in the common marmoset ( Callithrix jacchus)

Brain-stem auditory evoked potentials (BAEPs) were recorded in 10 common marmosets ( Callithrix jacchus) to investigate the effects of recording electrode configurations, stimulus rate, and stimulus frequency on BAEP wave forms and peak latencies. Tone burst stimulations were used to evaluate the effects of pure tone on BAEP wave forms. Five positive peaks superimposed on positive and negative slow potentials were identified in the BAEP recorded at the linkage between the vertex and the dorsal base of the ear ipsilateral to a monaural stimulus. When the reference electrode was placed at the ipsilateral mastoid or the neck, the amplitudes of positive and negative slow potentials and the incidence of wave I increased. There were no significant changes in peak latencies of BAEP waves with changes in stimulus rate from 5 to 20/s. It was possible to record the BAEPs in response to tone burst stimulations at frequencies extending from 0.5 to 99 kHz. Wave I appeared apparently at high stimulus frequencies; while waves III to V, at low frequencies. Wave II was recorded at frequencies ranging from 0.5 to 99 kHz and comprised a superposition of 2 or 3 potentials.

Unmasking of cortical SEP components by changes in stimulus rate: a topographic study

We performed topographic mapping of somatosensory responses to median nerve stimulation delivered at 2, 5 and 10 Hz. Parietal N20 was significantly attenuated in 10 Hz somatosensory evoked potentials (SEPs), while central P22 diminished between 2 and 5 Hz, remaining stable thereafter. The single component most affected by increasing stimulus rate was N30, which abated by more than 50% in 10 Hz SEPs, as compared with basal responses. N30 attenuation disclosed the existence of an earlier negative component, N24, which appeared as a notch on the N30 ascending slope in 2 Hz SEPs, but became a well-defined peak at higher stimulus rates. The N24 negativity was not significantly modified by stimulus rate; it had a parietal counterpart (P24) with the same peak latency and identical behavior during the experimental procedure. Both P24 and N24 could be differentiated from central P22 on the basis of topographical distribution and response to stimulus frequency. P22 topography could be the result of a radially oriented generator, while P24/N24 appeared as the two poles of a neural source tangential to the scalp. P27 was seen in 40% of the subjects only; it is suggested that P27 is itself a composite potential to which the generator of N30 could contribute in part. We conclude that there is no single “optimal” stimulation rate for SEP recording. On the contrary, combination of different frequencies of stimulation should enhance the diagnostic utility of this technique by allowing a more selective assessment of overlapping activities.

The effect of stimulus rate upon common peroneal, posterior tibial, and sural nerve somatosensory evoked potentials

We examined the effect of stimulus rate on somatosensory evoked potentials (SEPs) following stimulation of the common peroneal nerve (CPN) at the knee, and the posterior tibial nerve (PTN) and sural nerve (SN) at the ankle. We measured the amplitude of P40-N50 and N50-P60 in the PTN-SEP and corresponding amplitude of CPN-SEP and SN-SEP at the rate of 2.3, 3.4, 4.1, and 5.1 Hz. When the stimulation rate was increased from 2.3 to 5.1 Hz, the P40-N50 amplitude decreased by 50% for the CPN-SEP and 20% for the PTN-SEP. Also, the N50-P60 amplitude was reduced by 30% in the CPN-SEP and 20% in the PTN-SEP. In contrast, this change in stimulus rate produced no significant amplitude decline in the SN-SEP. Blocking the peroneal nerve with lidocaine just distal to the stimulating electrodes eliminated the descending peroneal nerve volley and abolished the amplitude attenuation observed with the faster stimulus rate. The findings suggest that at higher rates of stimulation, the afferent volleys induced by the movements that follow mixed nerve stimulation interfere with the SEP produced by electrical activation of the sensory afferents. The interference is greater when the more proximal site of the mixed nerve is stimulated.

O2 Sep subcomponents unmasked by changes in stimulus rate. A mapping study

O2 Sep subcomponents unmasked by changes in stimulus rate. A mapping study

Calcium flux in the mammalian ventricular myocardium.

The exchange of Ca(45) was studied in dog myocardium by means of a newly developed perfusion technique whereby an excised papillary muscle was perfused through its own artery. This makes possible the sequential and simultaneous correlation of ionic flux with ventricular myocardial function with each muscle serving as its own control. Calcium exchange has the following characteristics: (a) The major component of calcium flux is independent of the frequency of contraction. It demonstrates a rapidly equilibrating phase (half-time, 4 to 6 minutes) and a more slowly equilibrating phase with a progressively decreasing rate constant. The flux characteristics of the more rapidly equilibrating compartment are determined by a factor or factors, in addition to simple diffusion, which increase the time required for this compartment to achieve a steady-state with respect to the vascular compartment. (b) A lesser component of exchange is stimulus-rate dependent and is characterized by an alteration in the rate of calcium turnover such that the altered influx: efflux ratio requires 20 to 25 minutes to achieve equilibrium. After this time, despite the higher stimulus rate, there is no evidence of change in total tissue calcium. (c) The initial rate of the transient response is approximately proportional to the change in stimulus rate.