Range Of Interstimulus Intervals Research Articles

Spinally targeted paired associative stimulation with high-frequency peripheral component induces spinal level plasticity in healthy subjects

A novel variant of paired-associative stimulation (PAS) consisting of high-frequency peripheral nerve stimulation (PNS) and high-intensity transcranial magnetic stimulation (TMS) above the motor cortex, called high-PAS, can lead to improved motor function in patients with incomplete spinal cord injury. In PAS, the interstimulus interval (ISI) between the PNS and TMS pulses plays a significant role in the location of the intended effect of the induced plastic changes. While conventional PAS protocols (single TMS pulse often applied with intensity close to resting motor threshold, and single PNS pulse) usually require precisely defined ISIs, high-PAS can induce plasticity at a wide range of ISIs and also in spite of small ISI errors, which is helpful in clinical settings where precise ISI determination can be challenging. However, this also makes the determination of high-PAS level of plasticity induction more challenging and calls for more research on the mechanism of action of high-PAS. We sought to determine if the TMS-induced orthodromic activation in upper motor neurons and PNS-induced antidromic activation in lower motor neurons arriving simultaneously to the intervening synapses at the spinal cord level can be shown to induce acute changes at the targeted location, unlike an otherwise identical but cortically targeted equivalent. Ten healthy subjects participated in two separate sessions, where high-PAS induced activation was set to target spinal (SPINAL) or cortical (CORTICAL) levels with ISI manipulation between otherwise identically applied TMS and PNS pulses. The outcomes were assessed with motor-evoked potentials (MEPs) and Hoffmann (H)-reflex before (PRE), immediately after, and 30 and 60 min after (POST, POST30, POST60) the intervention. MEPs were significantly enhanced in both interventions. In the SPINAL but not in the CORTICAL session, maximal H-reflex amplitudes significantly increased at two timepoints, indicating an increase in spinal excitability. The H/M ratio (maximal H-reflex normalized to maximal M-wave) also showed a significant increase from PRE to POST30 timepoint in the SPINAL session when compared with the CORTICAL equivalent. These results confirm that spinally targeted high-PAS with individualized ISIs indeed has an effect at the spinal level in the sensorimotor system. High-PAS is a novel PAS variant that has shown promising results in motor rehabilitation of individuals with SCI and these new findings contribute to the understanding of its mechanism of action. This provides further evidence for high-PAS as an option for clinical settings to target plasticity at different levels of the corticospinal tract.

A Method for Electrical Stimulus Artifact Removal Exploiting Neural Refractoriness: Validation by Contrasting Cathodic and Anodic Stimulation.

To present a novel method for removing stimulus transient that exploits the absolute refractory period of electrically excitable neural tissues. Electrical stimulation often generates significant signal artifacts that can obscure important physiological signals. Removal of the artifact and understanding latent information from these signals could provide objective measures of circuit engagement, potentially driving advancements in neuromodulation research and therapies. We conducted intracranial physiology studies on five consecutive patients with Parkinson's disease who underwent deep brain stimulation (DBS) surgery as part of their routine care. Monopolar stimuli (either cathodic or anodic) were delivered in pairs through the DBS electrode across a range of inter-stimulus intervals. Recordings from adjacent unused electrode contacts used broadband sampling and precise synchronization to generate a robust template for the stimulus transient during the absolute refractory period. These templates of stimulus transient were then subtracted from recordings at different intervals to extract and analyze the residual neural potentials. After artifact removal, the residual signals exhibited absolute and relative refractory periods with timing indicative of neural activity. Cathodic and anodic DBS pulses generated distinct patterns of local tissue activation, showing phase independence from the prior stimulus. The earliest detectable neural responses occurred at short peak latencies (ranging from 0.19 to 0.38 ms post-stimulus) and were completely or partially obscured by the stimulus artifact prior to removal. Cathodic stimuli produced stronger local tissue responses than anodic stimuli, aligning with clinical observations of lower activation thresholds for cathodic stimulation. However, cathodic and anodic pulses induced artifact patterns that were equivalent but opposite. The proposed artifact removal technique enhances prior approaches by allowing direct measurement of local tissue responses without requirements for stimulus polarity reversal, template scaling, or specialized filters. This approach could be integrated into future neuromodulation systems to visualize stimulus-evoked neural potentials that would otherwise be obscured by stimulus artifacts.

Paired Associative Stimulation with Interstimulus Intervals of Short-latency Afferent Inhibition on Motor Plasticity

ABSTRACT Background: Short-latency afferent inhibition (SAI) is a method used to assess sensorimotor integration. Inhibition typically occurs at an interstimulus interval (ISI) of 20–22 ms or N20 + 2 ms. Paired associative stimulation (PAS) applied at certain ISIs consecutively can induce changes in corticospinal excitability. Usually, ISIs of 10 and 25 ms are applied in PAS. In this study, we aimed to investigate the relationship between ISIs of SAI and PAS, a neuromodulation paradigm. To achieve this, we first identified the optimal ISIs that produced maximum inhibition and facilitation during SAI by evaluating multiple ISIs. Subsequently, we applied the PAS paradigm with these ISIs. Materials and Methods: Twelve healthy participants were recruited for the study conducted over three sessions. During the first session, we examined the ISI of maximum inhibitory and ISI of facilitatory or minimum inhibitory (if facilitation was absent) in each participant at multiple ISIs. In the other two sessions, we applied PAS at the ISI of maximum inhibitory and the ISI of facilitatory or minimum inhibitory. We compared the motor-evoked potential (MEP) amplitudes before PAS, immediately after PAS, and 30 min after PAS. Results: The highest inhibition in SAI was observed at an ISI of 22 ms. In 60% of the participants, inhibition was most prominent at this ISI. Facilitation was not observed in 50% of the participants. During the PAS paradigm, which used the ISI of maximum inhibitory, significant facilitation was observed 30 min after the procedure compared with baseline (P = 0.011) and immediately post-PAS (P = 0.026). The mean MEP amplitude decreased significantly 30 min after the procedure compared with the baseline in ISI of only detected facilitation (P = 0.041). Conclusion: Our findings suggest that the ISI of maximum inhibition can vary among individuals, and that facilitation may not be observed in everyone within the ISI range of 22 ms to 40 ms. The results indicate that paired stimuli at ISI of maximum inhibitory in SAI increase corticospinal excitability. In addition, PAS at ISI of only facilitation decreases excitability. These changes in excitability may be explained by spike-timing-dependent plasticity.

Test-Retest Reliability of Short-Interval Intracortical Inhibition Assessed by Threshold-Tracking and Automated Conventional Techniques.

Two novel short-interval intracortical inhibition (SICI) protocols, assessing SICI across a range of interstimulus intervals (ISIs) using either parallel threshold-tracking transcranial magnetic stimulation (TT-TMS) or automated conventional TMS (cTMS), were recently introduced. However, the test-retest reliability of these protocols has not been investigated, which is important if they are to be introduced in the clinic. SICI was recorded in 18 healthy subjects using TT-TMS (T-SICI) and cTMS (A-SICI). All subjects were examined at four identical sessions, i.e., morning and afternoon sessions on 2 d, 5–7 d apart. Both SICI protocols were performed twice at each session by the same observer. In one of the sessions, another observer performed additional examinations. Neither intraobserver nor interobserver measures of SICI differed significantly between examinations, except for T-SICI at ISI 3 ms (p = 0.00035) and A-SICI at ISI 2.5 ms (p = 0.0103). Intraday reliability was poor-to-good for A-SICI and moderate-to-good for T-SICI. Interday and interobserver reliabilities of T-SICI and A-SICI were moderate-to-good. Although between-subject variation constituted most of the total variation, SICI repeatability in an individual subject was poor. The two SICI protocols showed no considerable systematic bias across sessions and had a comparable test-retest reliability profile. Findings from the present study suggest that both SICI protocols may be reliably and reproducibly employed in research studies, but should be used with caution for individual decision-making in clinical settings. Studies exploring reliability in patient cohorts are warranted to investigate the clinical utility of these two SICI protocols.

Short Interval Intracortical Inhibition Responses to Low-Frequency Repetitive Transcranial Magnetic Stimulation Under Multiple Interstimulus Intervals and Conditioning Intensities

The extent to which short interval intracortical inhibition (SICI) responds to low-frequency repetitive transcranial magnetic stimulation (rTMS) remains inconclusive with reports of increased, decreased and unchanged response following modulation. The aim of this study was to systematically investigate if the variability of SICI following rTMS is explained by the interstimulus interval (ISI) and/or the conditioning stimulus intensity (CSI). Two experiments with pretesting/posttesting and an rTMS session (1 Hz, 90% RMT, 900 pulses) were done. Experiment I (N = 15): SICI with multiple ISIs (1.0-4.0 msec, 0.2 msec increment). Experiment II (N = 15): SICI with CSIs (50-95% of RMT, 5% increment). In both experiments, the cortical silent period (cSP) was also collected. After low-frequency rTMS, no significant change (p > 0.10) in SICI at any specific ISI or CSI was observed, nor did the optimal ISI or CSI change. However, a significant decrease was observed in SICI responses when assessed under the range of ISIs (p = 0.0001), but not CSIs. cSP inhibition increased significantly (p < 0.0015) for both experiments. The optimal ISI or CSI did not shift or reveal SICI changes after inhibitory rTMS. However, when the whole curve of SICI responses were evaluated from a wide range of ISIs, a decrease in inhibition was found. The contrast between the results of individual ISI tests and the wide range of ISI assessment may be due to higher intersubject variability of SICI and/or sample size, rendering traditional SICI testing methods ineffective for measuring changes in inhibition. Further, it is possible that rTMS modulates GABAA and GABAB mediated inhibitory processes differently, which would explain the conflicting results for SICI and cSP.

Optimal inter-stimulus interval for paired associative stimulation with mechanical stimulation.

In this paper, inter-stimulus interval (ISI) of paired associative stimulation (PAS) with mechanical stimulation was analyzed. PAS is a prominent therapeutic intervention for individuals after stroke and helps to improve limb function by strengthening excitatory synapses and inducing neural plasticity. This intervention involves repeated application of transcranial magnetic stimulation (TMS) followed by peripheral stimulation. When responses to both stimulations are overlapped in the brain at the same time, this successful PAS is expected to induce long term potentiation (LTP) which leads to a neural plasticity phenomenon. Therefore ISI between these two stimulations is very crucial in this treatment. Instead of electrical stimulation in general PAS, mechanical stimulation was used in this study due to some promising aspects of mechanical stimulation. Long latency stretch response (LLSR) was observed in electromyography (EMG) during the PAS with mechanical stimulation, since LLSR reflects successful overlapping of two stimulations. Each subject had specific range of ISIs, or a time window, that leads to successful overlapping of paired stimulations. These time window lengths varied between 5ms and 105 ms, and within this range it can be guaranteed to obtain LLSR in EMG at least 40% among the all PAS trials. In addition, normally distributed responses within time window suggests that the optimal ISI which results in the highest number of LLSRs is the average of the time window. This result suggests that PAS with mechanical stimulation could lead to a rehabilitation effect by regaining motor functionality when the two stimulations are paired with the optimal ISI and it could provide a significant advancement in neuromodulation.

Paired Associative Stimulation with High-Frequency Peripheral Component Leads to Enhancement of Corticospinal Transmission at Wide Range of Interstimulus Intervals.

Background: In spinal paired associative stimulation (PAS), orthodromic and antidromic volleys elicited by transcranial magnetic stimulation (TMS) and peripheral nerve stimulation (PNS) coincide at corticomotoneuronal synapses at the spinal cord. The interstimulus interval (ISI) between TMS and PNS determines whether PAS leads to motor-evoked potential (MEP) potentiation or depression. PAS applied as a long-term treatment for neurological patients might alter conduction of neural fibers over time. Moreover, measurements of motoneuron conductance for determination of ISIs may be challenging in these patients.Results: We sought to design a PAS protocol to induce MEP potentiation at wide range of ISIs. We tested PAS consisting of high-intensity (100% stimulator output, SO) TMS and high-frequency (50 Hz) PNS in five subjects at five different ISIs. Our protocol induced potentiation of MEP amplitudes in all subjects at all tested intervals. TMS and PNS alone did not result in MEP potentiation. The variant of PAS protocol described here does not require exact adjustment of ISIs in order to achieve effective potentiation of MEPs.Conclusions: This variant of PAS might be feasible as a long-term treatment in rehabilitation of neurological patients.

A combined TMS-EEG study of short-latency afferent inhibition in the motor and dorsolateral prefrontal cortex.

Combined transcranial magnetic stimulation and electroencephalography (TMS-EEG) enables noninvasive neurophysiological investigation of the human cortex. A TMS paradigm of short-latency afferent inhibition (SAI) is characterized by attenuation of the motor-evoked potential (MEP) and modulation of N100 of the TMS-evoked potential (TEP) when TMS is delivered to motor cortex (M1) following median nerve stimulation. SAI is a marker of cholinergic activity in the motor cortex; however, the SAI has not been tested from the prefrontal cortex. We aimed to explore the effect of SAI in dorsolateral prefrontal cortex (DLPFC). SAI was examined in 12 healthy subjects with median nerve stimulation and TMS delivered to M1 and DLPFC at interstimulus intervals (ISIs) relative to the individual N20 latency. SAI in M1 was tested at the optimal ISI of N20 + 2 ms. SAI in DLPFC was investigated at a range of ISI from N20 + 2 to N20 + 20 ms to explore its temporal profile. For SAI in M1, the attenuation of MEP amplitude was correlated with an increase of TEP N100 from the left central area. A similar spatiotemporal neural signature of SAI in DLPFC was observed with a marked increase of N100 amplitude. SAI in DLPFC was maximal at ISI N20 + 4 ms at the left frontal area. These findings establish the neural signature of SAI in DLPFC. Future studies could explore whether DLPFC-SAI is neurophysiological marker of cholinergic dysfunction in cognitive disorders.

Assessment of nonlinear interactions in event-related potentials elicited by stimuli presented at short interstimulus intervals using single-trial data.

The recording of brain event-related potentials (ERPs) is a widely used technique to investigate the neural basis of sensory perception and cognitive processing in humans. Due to the low magnitude of ERPs, averaging of several consecutive stimuli is typically employed to enhance the signal to noise ratio (SNR) before subsequent analysis. However, when the temporal interval between two consecutive stimuli is smaller than the latency of the main ERP peaks, i.e., when the stimuli are presented at a fast rate, overlaps between the corresponding ERPs may occur. These overlaps are usually dealt with by assuming that there is a simple additive superposition between the elicited ERPs and consequently performing algebraic waveform subtractions. Here, we test this assumption rigorously by providing a statistical framework that examines the presence of nonlinear additive effects between overlapping ERPs elicited by successive stimuli with short interstimulus intervals (ISIs). The results suggest that there are no nonlinear additive effects due to the time overlap per se but that, for the range of ISIs examined, the second ERP is modulated by the presence of the first stimulus irrespective of whether there is time overlap or not. In other words, two ERPs that overlap in time can still be written as an addition of two ERPs but with the second ERP being different from the first. This difference is also present in the case of nonoverlapping ERPs with short ISIs. The modulation effect elicited on the second ERP by the first stimulus is dependent on the ISI value.

Is neural adaptation of the N170 category-specific? Effects of adaptor stimulus duration and interstimulus interval

Neural adaptation paradigms have been used in the electrophysiological and neuroimaging literature to characterise neural populations underlying face and object perception. It was recently reported by Nemrodov and Itier (2012) that adaptation of the N170 event-related potential (ERP) component is not stimulus category-specific over rapid adapting stimulus durations (S1 durations) and interstimulus intervals (ISIs). We therefore tested the category-specificity of adaptation over a range of S1 durations and ISIs. Faces and chairs were presented at S1 (for 200, 500 or 1000ms) and S2 (for 200ms), over a variable ISI (200 or 500ms). Mean amplitudes of the P1, N170 and P2 visual ERP components were measured following S1 and S2 stimuli. Faces at S1 led to the smallest (i.e., most adapted) N170 amplitudes to both faces and chairs at S2, more than chairs at S1. N170s at S2 were smallest after a 500ms S1 duration; but N170 amplitude did not vary over ISI. Effects were also seen for the two surrounding positive components, the P1 and P2. Presenting faces at S1 led to enhanced P1 amplitudes evoked by S2 chair stimuli. The P2 showed the smallest amplitudes following the shorter 200ms ISI. These results indicate that adaptation of the N170 is not actually category-specific but instead dependent on the S1 category (regardless of S2 category), and may also be influenced by earlier effects at the P1 (i.e., not specific to the N170). This challenges the assumption that N170 category adaptation indexes effects on distinct neural populations that differ between faces and non-face objects.

Opposite effects of weak transcranial direct current stimulation on different phases of short interval intracortical inhibition (SICI)

Short interval intracortical inhibition (SICI) is a common paired-pulse TMS technique that is used to measure GABAa-ergic inhibition in the cerebral motor cortex. However, inhibition evaluated with an interstimulus interval (ISI) between the TMS pulses of 2.5ms has quite different properties from that seen at 1ms. It is thought that the latter may represent either (or both) a different type of synaptic inhibition or refractoriness of neural membranes. The present experiments provide further evidence about the early and late components of SICI using transcranial direct current stimulation (tDCS), a technique thought to change neural excitability by polarising the nerve membranes. We assessed SICI using a threshold tracking method at a range of ISIs during concurrent application of tDCS in 11 healthy volunteers (8 males, 27-43years old). Each subject underwent both anodal and cathodal tDCS with two different intensities of stimulation (1 and 2mA). Because there was no significant difference between the results at the two intensities, the data were combined. Principal component analysis was used to separate the contributions of early and late SICI to the time course of inhibition from 1 to 5ms tDCS had opposite effects on early and late SICI. Anodal tDCS reduced late SICI but enhanced early SICI, whereas cathodal tDCS had the opposite effect. This is further evidence that the two phases of SICI are produced by different mechanisms, perhaps involving different sets of neurones or different locations on the same neurone that respond oppositely to tDCS.

Masked Priming Effects in Aphasia: Evidence of Altered Automatic Spreading Activation

Previous research has suggested that impairments of automatic spreading activation may underlie some aphasic language deficits. The current study further investigated the status of automatic spreading activation in individuals with aphasia as compared with typical adults. Participants were 21 individuals with aphasia (12 fluent, 9 nonfluent) and 31 typical adults. Reaction time data were collected on a lexical decision task with masked repetition primes, assessed at 11 different interstimulus intervals (ISIs). Masked primes were used to assess automatic spreading activation without the confound of conscious processing. The various ISIs were used to assess the time to onset and duration of priming effects. The control group showed maximal priming in the 200-ms ISI condition, with significant priming at a range of ISIs surrounding that peak. Participants with both fluent and nonfluent aphasia showed maximal priming effects in the 250-ms ISI condition and primed across a smaller range of ISIs than did the control group. Results suggest that individuals with aphasia have slowed automatic spreading activation and impaired maintenance of activation over time, regardless of fluency classification. These findings have implications for understanding aphasic language impairment and for development of aphasia treatments designed to directly address automatic language processes.

Does a sensory processing deficit explain counting accuracy on rapid visual sequencing tasks in adults with and without dyslexia?

The experiments conducted aimed to investigate whether reduced accuracy when counting stimuli presented in rapid temporal sequence in adults with dyslexia could be explained by a sensory processing deficit, a general slowing in processing speed or difficulties shifting attention between stimuli. To achieve these aims, the influence of the inter-stimulus interval (ISI), stimulus duration, and sequence length were evaluated in two experiments. In the first that used skilled readers only, significantly more errors were found with presentation of long sequences when the ISI or stimulus durations were short. Experiment 2 used a wider range of ISIs and stimulus durations. Compared to skilled readers, a group with dyslexia had reduced accuracy on two-stimulus sequences when the ISI was short, but not when the ISI was long. Although reduced accuracy was found on all short and long sequences by the group with dyslexia, when performance on two-stimulus sequences was used as an index of sensory processing efficiency and controlled, group differences were found with presentation of stimuli of short duration only. We concluded that continuous, repetitive stimulation to the same visual area can produce a capacity limitation on rapid counting tasks in all readers when the ISIs or stimulus durations are short. While reduced accuracy on rapid sequential counting tasks can be explained by a sensory processing deficit when the stimulus duration is long, slower processing speed in the group with dyslexia explains the greater inaccuracy found as sequence length is increased when the stimulus duration is short.

The crossmodal facilitation of visual object representations by sound: Evidence from the backward masking paradigm.

We report a series of experiments designed to demonstrate that the presentation of a sound can facilitate the identification of a concomitantly presented visual target letter in the backward masking paradigm. Two visual letters, serving as the target and its mask, were presented successively at various interstimulus intervals (ISIs). The results demonstrate that the crossmodal facilitation of participants' visual identification performance elicited by the presentation of a simultaneous sound occurs over a very narrow range of ISIs. This critical time-window lies just beyond the interval needed for participants to differentiate the target and mask as constituting two distinct perceptual events (Experiment 1) and can be dissociated from any facilitation elicited by making the visual target physically brighter (Experiment 2). When the sound is presented at the same time as the mask, a facilitatory, rather than an inhibitory effect on visual target identification performance is still observed (Experiment 3). We further demonstrate that the crossmodal facilitation of the visual target by the sound depends on the establishment of a reliable temporally coincident relationship between the two stimuli (Experiment 4); however, by contrast, spatial coincidence is not necessary (Experiment 5). We suggest that when visual and auditory stimuli are always presented synchronously, a better-consolidated object representation is likely to be constructed (than that resulting from unimodal visual stimulation).

Using paired pulse TMS to facilitate contralateral and ipsilateral MEPs in upper extremity muscles of chronic hemiparetic stroke patients

In moderate to severely impaired stroke patients, single pulse TMS, with or without background facilitation, may not be able to evoke a motor response in muscles of the upper extremity, thereby hindering potential studies of stroke patients using TMS. Paired pulse TMS has been shown to facilitate responses in distal muscles of healthy subjects. In this study, our aim was to investigate thirteen muscles of the upper extremity in moderate to severely impaired stroke patients and determine the paired pulse interstimulus interval (ISI) that was optimal for facilitation of the TMS response. MethodsWe recruited 8 moderate to severely impaired stroke patients and 5 healthy controls. A hotspot was found that could activate the greatest number of the 13 target upper extremity muscles. 16 ISIs were tested. ResultsIn healthy controls, an ISI range of 3–50ms in the left hemisphere and 8–40ms in the right hemisphere was optimal for activating the contralateral arm. In the stroke patients, stimulation of the non-lesioned hemisphere at an ISI of 8–50ms was optimal for contralateral responses, similar to the control subjects, while stimulation of the lesioned hemisphere had an optimal ISI range of 12–50ms. Ipsilateral responses in the paretic limb were frequent and the optimal ISI range was much later than the contralateral responses in stroke or controls occurring at 25–40ms. ConclusionIn stroke and control subjects, across muscles and contralateral or ipsilateral pathways, an interstimulus interval of 25–40ms was optimal to evoke a TMS response and resulted in the greatest degree of facilitation.

Apparent motion distorts the shape of a stimulus briefly presented along the motion path

We examined whether motion blur accompanying apparent motion (AM) affects the shape of a stimulus presented in the motion path. In a two-alternative forced-choice procedure, observers judged the shape of a Gaussian test stimulus flashed in the path of motion, relative to a reference stimulus, which was a circular Gaussian stimulus located away from the path of motion. In Experiment 1, we report that the test stimulus was affected by AM and its perceived width was wider than its actual width, and counteracting this distortion, shape discrimination thresholds coincided with a test stimulus that was physically "thinner" than the reference stimulus. Shape distortion correlated with the strength of AM (Experiment 2) and increased within the range of inter-stimulus intervals used to induce AM and with retinal eccentricity but was eliminated when the test stimulus was made "hard-edged" (Experiment 3) or when the stimulus does not overlap with the motion path (Experiment 4). In Experiment 5, we demonstrate that the effect is present for dichoptic presentations. These results can be accounted for by a process in which the neural representation of AM generated by higher cortical areas feedback to interfere with the coding of stimulus shape by units located along the trajectory of AM.

Orientation Anisotropy in the Ternus Phenomenon

The Ternus display is an ambiguous, multi-element, apparent-movement animation which can be perceived in two alternative organizations. One of these involves the simultaneous movement of several elements and is called group movement. The other involves the movement of one element only and is called element movement. The present study examined the influence of retinal eccentricity and organizational orientation on the percentage of group-movement reports obtained across a range of interstimulus intervals. Six participants observed 48 variations of the Ternus display over 100 replications and judged the type of movement seen on each trial. Analysis showed that retinal eccentricity had no effect on the appearance of the display. However, compared with horizontally organized elements, obliquely organized and vertically organized elements yielded progressively more group movement across all but the shortest interstimulus intervals. These results represent an orientational anisotropy in the processing of Ternus apparent movement.

Interaction between the effects of corticotropin-releasing factor and prepulse parameters on prepulse inhibition in two inbred rat strains and the F1 generation of a cross between them

Levels of prepulse inhibition (PPI) depend on the interval between the startling and prepulse stimuli. Brown Norway rats show less PPI of the acoustic startle response than Wistar–Kyoto (WKY) rats when the interval between the prepulse and startling stimulus is 100 ms. Central administration of corticotropin-releasing factor (CRF) decreases PPI at this inter-stimulus interval. Here, the effect of CRF on PPI over a range of inter-stimulus intervals was examined in WKY and BN rats, and in the F1 generation of a cross between them. Rats received an intracerebroventricular infusion of either saline or CRF 30 min prior to testing PPI. Test trials included startle stimulus alone trials, and trials on which a prepulse stimulus of either 6, 12, or 15 dB above background preceded the startling stimulus by either 20, 75, 100, 500 or 2000 ms. CRF decreased PPI in WKY rats at all inter-stimulus intervals and all prepulse intensities, while the effect of CRF on PPI in BN rats only occurred at intermediate intervals. BN and WKY rats showed different levels of PPI only at the intermediate intervals. Baseline PPI in the F1 rats resembled the WKY phenotype. The CRF-induced change in PPI in the F1 generation has some qualities of the effects in each of the progenitor strains. These results suggest that both the effect of rats strain and of CRF on PPI depend on the inter-stimulus interval, and that there is an interaction between prepulse stimulus intensity and the inter-stimulus interval.

Does the sight of physical threat induce a tactile processing bias?: Modality-specific attentional facilitation induced by viewing threatening pictures

Threatening stimuli are thought to bias spatial attention toward the location from which the threat is presented. Although this effect is well-established in the visual domain, little is known regarding whether tactile attention is similarly affected by threatening pictures. We hypothesised that tactile attention might be more affected by cues implying physical threat to a person's bodily tissues than by cues implying general threat. In the present study, participants made temporal order judgments (TOJs) concerning which of a pair of tactile (or auditory) stimuli, one presented to either hand, at a range of inter-stimulus intervals, had been presented first. A picture (showing physical threat, general threat, or no threat) was presented in front of one or the other hand shortly before the tactile stimuli. The results revealed that tactile attention was biased toward the side on which the picture was presented, and that this effect was significantly larger for physical threat pictures than for general threat or neutral pictures. By contrast, the bias in auditory attention toward the side of the picture was significantly larger for general threat pictures than for physical threat pictures or neutral pictures. These findings therefore demonstrate a modality-specific effect of physically threatening cues on the processing of tactile stimuli, and of generally threatening cues on auditory information processing. These results demonstrate that the processing of tactile information from the body part closest to the threatening stimulus is prioritized over tactile information from elsewhere on the body.

Are Age Differences in Verbal Learning Related to Interstimulus Interval and Education?

The present study investigated the effects of a narrow range of interstimulus intervals (ISI; 1, 2, or 3 s) on word-learning performance in relation to age and education. Individuals (N = 338) from four age groups (24 to 76 years) with low or high educational attainment were randomly assigned to one of three ISI conditions. Older age, lower education, and shorter ISI each led to lower performance. However, age differences in performance were not affected by ISI. Furthermore, lower educated individuals needed more time to achieve the same performance level as higher educated individuals.