Sec Interstimulus Interval Research Articles

Habituation of Backward Escape Swimming in the Marbled Crayfish.

In the present study, we performed behavioral analyses of the habituation of backward escape swimming in the marbled crayfish, Procambarus fallax. Application of rapid mechanical stimulation to the rostrum elicited backward swimming following rapid abdominal flexion of crayfish. Response latency was very short-tens of msec-suggesting that backward swimming is mediated by MG neurons. When stimulation was repeated with 10 sec interstimulus intervals the MG-like tailflip did not occur, as the animals showed habituation. Retention of habituation was rather short, with most animals recovering from habituation within 10 min. Previous experience of habituation was remembered and animals habituated faster during a second series of experiments with similar repetitive stimuli. About half the number of stimulus trials was necessary to habituate in the second test compared to the first test. This promotion of habituation was observed in animals with delay periods of rest within 60 min following the first habituation. After 90 min of rest from the first habitation, animals showed a similar time course for the second habituation. With five stimuli at 15 min interval during 90 min of the rest, trained animals showed rapid habituation, indicating reinforcement of the memory of previous experiments. Crayfish also showed dishabituation when mechanical stimulation was applied to the tail following habituation.

Amplitude-dependency of response of SI cortex to flutter stimulation

BackgroundIt is established that increasing the amplitude of a flutter stimulus increases its perceived intensity. Although many studies have examined this phenomenon with regard to the responding afferent population, the way in which the intensity of a stimulus is coded in primary somatosensory cortex (SI) remains unclear.ResultsOptical intrinsic signal (OIS) imaging was used to study the evoked responses in SI of anesthetized squirrel monkeys by 25 Hz sinusoidal vertical skin displacement stimulation. Stimuli were 10 sec duration with a 50 sec inter-stimulus interval. Stimulus amplitude ranged from 50 to 400 microns and different amplitudes were interleaved. Control levels of activity were measured in the absence of stimulation, and used to compare with activation levels evoked by the different stimulus amplitudes. Stimulation of a discrete skin site on the forelimb evoked a prominent increase in absorbance within the forelimb representational region in cytoarchitectonic areas 3b and 1 of the contralateral hemisphere. An increase in stimulus amplitude led to a proportional increase in the magnitude of the absorbance increase in this region of areas 3b and 1 while surrounding cortex underwent a decrease in absorbance. Correlation maps revealed that as stimulus amplitude is increased, the spatial extent of the activated region in SI remains relatively constant, and the activity within this region increases progressively. Additionally, as stimulus amplitude is increased to suprathreshold levels, activity in the surround of the activated SI territory decreases, suggesting an increase in inhibition of neuronal activity within these regions.ConclusionIncreasing the amplitude of a flutter stimulus leads to a proportional increase in absorbance within the forelimb representational region of SI. This most likely reflects an increase in the firing rate of neurons in this region of SI. The relatively constant spatial extent of this stimulus-evoked increase in absorbance suggests that an increase in the amplitude of a 25 Hz skin stimulus does not evoke a larger area of SI neuronal activation due to an amplitude-dependent lateral inhibitory effect that spatially funnels the responding SI neuronal population.

Auditory cortical response patterns to multiple rhythms of AM sound.

Multiple amplitude modulation (AM) of a tone results in a time series with a complex structure of envelope fluctuations. In this study the cortical responses elicited by such an auditory stimulus were investigated. It was hypothesized that the auditory cortex responds simultaneously with different patterns of activity corresponding to the different rhythm of periodical stimulus fluctuations. The relations of these response patterns to either steady-state responses (SSR) in the 40 Hz range or the transient slow auditory evoked responses were investigated. Auditory evoked magnetic fields were recorded from the left temporal cortex of nine healthy humans in response to 250 Hz tones that were amplitude modulated with the sum of two sinusoids of 38 and 40 Hz. The stimulus was presented continuously to the subject's right ear at the intensity of 70 dB sensation level. In addition, the responses to 250 Hz tone-burst stimuli with duration of 20, 50, 100, and 200 msec, respectively, were recorded. The tone-bursts were presented at an inter-stimulus interval (ISI) of 0.5 sec, which was equivalent to the slowest rhythm of the multiple-AM stimulus. Magnetic source analysis was applied to all elicited waveforms. From all subjects SSR at 38 and 40 Hz were clearly recognizable and were superimposed by a periodical response pattern corresponding to 2 Hz stimulus envelope fluctuations. A positive peak with latency of 70 msec was the mostly pronounced response to tone-burst stimulation at the ISI of 0.5 sec and resembles the low-frequency response pattern to the AM stimulus. The N1-P2 complex showed an almost complete suppression at 0.5 sec ISI. In contrast, it was the most prominent evoked response activity when using a longer ISI of 3 sec. Source locations in overlapping areas were estimated for the SSR in the 40 Hz range, the prominent peak of low-frequency response to the AM stimulus, and the P1 peak at tone-burst stimulation, respectively. These were separated from the N1 source location by about 0.5 cm in anterior and 0.5 cm in medial direction. As a result of multiple AM the stimulus signal envelope fluctuates with frequencies of 2 Hz and around 40 Hz. The auditory cortex responds to this stimulus with different response patterns. Both modulation signals at 38 and 40 Hz were almost linearly represented as steady-state responses. The evoked response patterns to stimulus fluctuations at low-frequency rhythm resemble the slow cortical auditory evoked responses. The 2 Hz stimulus rhythm is perceived as loudness fluctuation, and 40 Hz modulation is perceived as a rough sound. It is assumed that the different cortical representations correspond to both types of perception of the complex AM sound.

Contrast transfer characteristics of visual short-term memory.

A two interval forced choice constant stimuli method was used to determine: (i) the point of subjective equality (PSE); and (ii) the just-noticeable-difference (JND) in contrast for two luminance gratings, one held in short-term visual memory. Psychometric functions for delayed contrast discrimination were determined as a function of spatial frequency from 1 to 8 c/deg, reference contrast from 5 to 60% and inter-stimulus interval from 1 to 10 sec. The PSE for remembered contrast was invariant with spatial frequency and inter-stimulus interval for the three reference contrast levels tested. The JND contrast plotted against spatial frequency followed a U-shaped function with lowest thresholds at around 4 c/deg. The threshold function translates parallel to the sensitivity axis with an increase in either the reference contrast or the inter-stimulus interval. However, the bandpass shape of the threshold function is invariant with both reference contrast and inter-stimulus interval. At 1, 3 and 10 sec inter-stimulus intervals, contrast JNDs increase with reference contrast according to a power law with an average exponent of 0.70. Contrast JNDs also increase as a power function of the inter-stimulus interval with an average exponent of 0.38 for the three reference contrasts tested.

Role of prefrontal cortex in generation of the contingent negative variation.

The contingent negative variation (CNV) is a brain potential generated during delay periods that has been proposed to measure prefrontal cortex (PFCx) activity. The CNV was recorded in neurological patients with PFCx damage centered in Brodmann areas 9, 44, 45, and 46 in a classical auditory S1-S2 paradigm employing a 3 sec interstimulus interval. Subjects pressed a button upon detection of an acoustically cued imperative tone (S2, 1000 Hz, GO). Responses were withheld if the warning tone (S1, 1500 Hz in GO trials) was lower in frequency (500 Hz, NOGO). The early phase of the CNV (500-700 msec after S1) was not reduced in patients with PFCx damage. PFCx lesions reduced the later phase of the CNV beginning about 1000 msec prior to S2. Reductions were maximal over PFCx sites but extended to posterior scalp electrodes over the lesioned hemisphere. The results are consistent with a late CNV generator in dorsolateral PFCx that also modulates generation of the potential in posterior regions of the ipsilateral hemisphere. The CNV findings coupled with behavioral evidence of impaired preparatory processes in these patients support the role of PFCx in sustaining distributed neural activity during delay periods.

Mismatch negativity area and age-related auditory memory

The deviant tones embedded in a sequence of standard tones elicit an event-related potential (ERP) component called mismatch negativity (MMN). Because MMN is partly overlapped by other ERP components at 100–200 msec latency (N1 and P2) and its shape varies, MMN peak latency and amplitude may be ambiguous. We used the difference area between the deviant and standard ERP to evaluate the age and interstimulus interval (ISI) dependence of MMN. Sequences of standard (85%) and deviant (15%) tones were presented to 27 normal subjects (age 18–85 years) using 1 sec and 3 sec ISIs and to 6 young subjects using an additional ISI of 5 sec. With this method MMN was clearly seen in 26 out of 27 healthy subjects (96.3%). MMN area was quite stable regardless of age with 1 sec ISI. With 3 sec ISI MMN area was significantly smaller in the old than in the young subjects. This may reflect the shortening of the sensory auditory memory trace with increasing age.

Delayed pattern discrimination in patients with unilateral temporal lobe damage

Behavioral and neurophysiological studies in macaque monkeys suggest a role of the inferior temporal cortex in pattern discrimination and visual memory. To determine whether this cortical area is also involved in human short-term visual memory, we measured spatial frequency discrimination thresholds for sequentially presented stimuli in 17 patients with unilateral, postoperative focal damage to the temporal cortex (11 left, 6 right hemisphere). These results are compared to those of 17 age-matched control subjects. Contrast detection thresholds and difference thresholds for spatial frequency were determined for spatially truncated sine wave gratings presented in the left and right visual fields. Detection thresholds were measured for sine wave gratings in a spatial two-alternative forced-choice procedure for three spatial frequencies [2.5, 5, and 10 cycles (c)/degree] for each hemifield. Discrimination thresholds were determined for two gratings sequentially presented either 4 degrees to the left or right of fixation. Grating contrast was five times the value of detection threshold and reference frequency was 5 c/degree. Within each trial, the gratings were separated in time by 1, 3, and 10 sec interstimulus intervals (ISIs), and subjects signaled which grating had the higher spatial frequency. The results indicate that (1) contrast detection thresholds overall did not differ between patient and control groups; (2) spatial frequency discrimination thresholds were, however, significantly elevated in patients and this elevation was significantly more pronounced in the visual field contralateral to the damaged hemisphere; and (3) patients with inferotemporal damage exhibited higher discrimination thresholds for the longest ISI, whereas patients with medial/superior temporal lobe damage did not show this effect. The results suggest that visual areas in human temporal cortex are involved in the higher visual processes underlying delayed pattern discrimination.

Reaction times measured in a choice reaction time and a double task condition: A small twin study

A genetic analysis of simple reaction times (RT) measured in young twins is reported. Reaction times were obtained in a choice RT task with varying interstimulus intervals and in a mixed task condition that consisted of the same choice RT trials and of double task trials, where subjects simultaneously performed mental arithmetic and the choice RT task. All RT measures showed significant influence of common environment. Heritabilities were task dependent: for the choice RT task higher heritabilities were seen for shorter (2 and 3 sec) than for longer (4 and 5 sec) interstimulus intervals. In the mixed condition heritabilities of almost 50% were seen for RT measured in double task trials, whereas no genetic influence was observed for choice RT trials (3 and 5 sec interstimulus interval) in this condition.

Long-latency event-related potentials in squirrel monkeys: further characterization of wave form morphology, topography, and functional properties

Event-related potentials (ERPs) were recorded from the brain surface of untrained monkeys exposed to sequences of auditory stimuli (2 kHz and 6 kHz tones of 40 msec duration). Stimulus probability and interstimulus interval (ISI) were systematically varied in different paradigms. In an oddball paradigm with a 1 sec ISI in which one stimulus constituted 90% of all trials and the other 10%, a “monkey” late positive component (MLPC), characterized by two peaks (P248 and P369), was recorded prominently over lateral parietal areas in response to the unpredictable and infrequent shifts in pitch. The amplitude of this late positivity was found to be sensitive to stimulus probability and to exhibit trial-to-trial sequential dependencies similar to those described for the human P300. The amplitude of MLPC was also found to be larger following longer ISIs. In addition, a ‘monkey’ late negative component (MLNC), with characteristics similar to those of the human slow wave (SW), was recorded following the infrequent shifts in pitch and found to temporally overlap with MLPC. MLNC was recorded with maximal amplitude over frontal cortex and was sensitive to stimulus probability but not to trial-to-trial changes in stimulus sequence. Thus MLPC and MLNC which appear to reflect similar yet distinct processes exhibit several analogies to the human P3a and SW, respectively.

Development of learning and memory in Aplysia. II. Habituation and dishabituation

The defensive withdrawal reflex of the mantle organs of Aplysia californica exhibits a variety of forms of both nonassociative and associative learning, which can exist in both short- and long-term forms. In addition, the reflex can be readily elicited and quantified as soon as the effector organs (siphon and gill) emerge at their respective developmental stages. Thus, this reflex system provides a useful preparation in which to study the development of learning and memory. In the present series of experiments we investigated the development of 2 forms of nonassociative learning, habituation and dishabituation, in the siphon withdrawal component of the reflex. This reflex response could be examined throughout the juvenile life of the animal (stages 9-12) since the reflex is functionally intact as soon as the siphon emerges in stage 9 (Rankin et al., 1987). We studied the development of habituation in stages 9-12 using tactile stimuli to the siphon delivered at interstimulus intervals (ISIs) of 1, 5, 10, and 30 sec. Habituation of siphon withdrawal was evident as early as juvenile stage 9. However, it existed in an immature form: Significant habituation was produced only with a very short (1 sec) ISI. No significant habituation occurred in response to 5 or 10 sec ISIs. Approximately 4 d later, in stage 10, significant habituation occurred to both 1 and 5 sec ISIs but not to a 10 sec ISI. Finally, approximately 1-2 weeks later, in stage 11, significant habituation occurred to 1, 5, and 10 sec ISIs but not to a 30 sec ISI, whereas stage 12 juveniles and adults (stage 13) readily habituated to a 30 sec ISI. Thus, there was a systematic developmental trend in the ability of the animals to habituate: Progressively older animals were capable of habituation to stimuli presented at progressively longer intervals. The systematic development of habituation was also evident by examining the amount of habituation exhibited to comparable ISIs by animals at different developmental stages. For all 4 ISIs examined, older animals showed significantly greater habituation than younger animals. Thus, our results show that habituation is present as soon as the siphon response system emerges and that it develops progressively throughout the juvenile life of the animal. Whereas habituation was present in the earliest developmental stage we examined (stage 9), dishabituation (in response to tail shock) did not emerge until 4-7 d later, in stage 10.(ABSTRACT TRUNCATED AT 400 WORDS)

A correlation study of contingent negative variation, reaction time, and EEG power spectrum in control and psychopathological populations

Contingent negative variation (CNV), reaction time (RT), and EEG power spectrum were measured in a group of 27 neurotics and 26 controls subjects, male and female, aged 18 to 38. CNV was recorded with a 1 sec interstimulus interval and averaged over 48 trials. Two spectral analyses of the EEG were performed, the first during the 1 sec period preceding S1 (spontaneous EEG), the second during the S1–S2 interval (activated EEG). For each group of subjects, we calculated the correlations between four measures of CNV amplitude, RT duration, and the relative powers of the delta, theta, alpha and beta activities during spontaneous and activated EEG. In neurotic subjects there was an absence of correlation between the pre- and post-imperative segments of the CNV, and between early CNV amplitude and per cent alpha power. Both groups shared in common strong correlations relating CNV amplitude and RT length, on the one hand, and the different components of the EEG spectrum, on the other hand, Principal component analysis applied to the pooled data revealed different factors for CNV and EEG parameters, suggesting independence of the neurophysiological mechanisms implied in the two phenomena.

Attention effects on auditory EPs as a function of inter-stimulus interval

The present study focuses on the effect of the duration of the inter-stimulus interval (ISI) on the ‘processing negativity’, the endogeneous negative brain potential elicited by attended stimuli in various selective-attention paradigms. Three constant ISIs are used, 250 msec, 800 msec, and 2000 msec, in a selective dichotic-listening situation in which the subject's task is to detect occasional slight pitch changes in the input to a designated ear. Frontal (Fz), vertex (Cz), and parietal (Pz) evoked potentials (EP) are recorded. The processing negativity is observed in each condition, even in that involving the 2 sec ISI, which is in contrast with the commonly held view that this attention effect is only obtained with very short ISIs. The processing negativity was observed to have two components: (1) an early, central component of small amplitude which appears to be independent of the ISI; (2) a later, frontal component of large amplitude and long duration which is certainly elicited with long ISIs such as the 800 msec and 2000 msec ISIs used here, but also appears to be present even in the short-ISI condition overlapping the central component. This suggests that it is the frontal component which is sensitive to the ISI.

Slow potential shifts of human brain during forewarned reaction

The slow brain potentiels observed during the 4 sec interstimulus interval (ISI) of a CNV paradigm were investigated by a factorial manipulation of the parameters that have been identified as affecting the CNV at ISIs of 1 or 2 sec. Subjects performed choice and simple reaction time (RT) tasks under all possible combinations of auditory and visual warning (S1) and imperative (S2) stimuli. The choice task involved easy or difficult intensity discriminations at S2, which were forewarned by S1s that cued the subject as to the level of difficulty for that trial. Principal components analysis (PCA) of the data revealed two negative afterwave factors and a late positive component (LPC) related to warning stimulus variables, and a late negative shift preceding S2 that was related to motor preparation. The negative afterwave components were enhanced in the choice RT task, and the earlier of the two components showed a modality-specific distribution. The LPC factor was also enhanced in the choice task and was further enhanced by S1s signaling difficult discriminations. Additionally, the LPC was larger for visual S1s. The S1-related components are interpreted in terms of orienting, while the later shift is identified with the readiness potential and motor preparation. The results support the notion that the conventionally recorded CNV consists of S1 evoked and response-related potentials rather than non-specific and modality-specific anticipatory potentials.

Evolution of negative and positive SP shifts in cats learning RT tasks

Cortical slow potential (SP) shifts were recorded in freely moving cats while they learned reaction time tasks differing in the duration of the inter-stimulus interval (ISI). ISI durations were either 6 or 4 sec in experiment I; in experiment II, a reaction time paradigm with a 1 sec ISI was compared to a time estimation task. SP shifts of opposite polarity development throughout the experiments. It seems that: (1) positive SP shifts reflect motor processes and mechanisms of proprioceptive feedback related to the cat's preparatory movements for pressing the lever; (2) negative-going shifts peaking at the end of the ISI reflect temporal information processing related to ISI duration. Analogies with potentials found in man and animals in similar paradigms are discussed.

Event-related potentials in schizophrenics

Fifteen schizophrenics and 15 age-matched controls were compared on 3 auditory event-related potential (ERP) paradigms that elicited a variety of components. In one paradigm, tones were given at 0.75, 2.25 and 6.75 sec interstimulus intervals; in another, infrequently occurring targets in a reaction-time task were interspread with frequent background stimuli; and, in a third, noise bursts or tones were delivered in a random sequence at either 70 or 100 dB SPL. The sensitivity of some of the ERP components in distinguishing schizophrenics from controls depended on the conditions under which the component was elicited. N1 amplitude was smaller in the schizophrenics than in the controls after longer interstimulus intervals. P2 amplitude was smaller in the schizophrenics only at higher stimulus intensities. P2 latency was shorter in schizophrenics except in the paradigm that varied interstimulus intervals. P3 amplitude, however, was much smaller in schizophrenics than controls regardless of whether P3 was elicited by targets in a task or was elicited by 100 dB SPL stimuli. The loud stimuli also elicited blink reflexes that coincided with N1, but these reflexes did not vary by clinical group. Neither the amplitude of the slow wave following targets nor the sustained potential that accompanies prolonged auditory stimuli differed between schizophrenics and controls.

Latency of multiple skin conductance responses in differential classical conditioning

Latencies of multiple skin conductance responses were observed in 30 female undergraduate students who participated in a classical differential conditioning experiment employing a 10 sec interstimulus interval (ISI). Responses occuring in both the early and late portions of the ISI were examined. Pairing delayed the onset of early responses and hastened the onset of responses occuring later in the ISI. Additionally, the latency changes observed did not appear to be an artifact of the higher response frequencies typically associated with conditioning.

Effects of warning-signal modality on the contingent negative variation (CNV)

CNVs were recorted during the S 1S 2 interval of a prolonged simple reaction task. In this task, a warning stimulus S 1 is followed by an imperative stimulus S 2, to which the subject makes motor response. The differential effects of a visual and an auditory S 1 were investigated under two interstimulus interval (ISI) durations (1 and 3 sec). Under the 3 sec ISI condition, the form of the slow negative wave demonstrated clearly a biphasic character: an orientation wave (O wave) following S 1 with a peak latency at about 650 msec and an expectancy wave (E wave), which reaches its largest amplitude towards the end of the ISI. Under the 1 sec ISI condition the two components of the CNV are confounded. The O wave had a frontocentral distribution, while the E wave was located precentrally. The O wave was enhanced after an auditory S 1, as compared to a visual S 1].

Heart-rate decelerative Pavlovian conditioning with tilt as UCS: Towards behavioural control of cardiac dysfunction

As part of a programme the ultimate goal of which is to teach behavioural control of stress-induced maladaptive cardiac accelerations through Pavlovian decelerative conditioning, this study was directed at examining the feasibility of using tilting of the body from a head-up to a head-down position as the unconditional stimulus (UCS) to elicit phasic cardiac deceleration as the unconditional response (UCR). Experiment I assessed the reflexive features of the cardiac response to 32 tilt UCS trials delivered at mean intervals of 75 sec. The results yielded a large-magnitude (over 30 BsPM) cardiac decelerative UCR with fast recruitment and complete resistance to habituation. Experiment II examined the feasibility of using the tilt UCS to demonstrate associative control over decelerative responding to a tone as the conditional stimulus (CS). Relative to a control ‘backward’ UCS-CS group with an interstimulus interval (ISI) of 14.5 sec, a 0.5 sec ISI CS-UCS experimental group demonstrated both orderly acquisition and extinction performance. The magnitude of the conditional deceleration of some 4 BsPM is greater than the extent of control generally achieved with biofeedback, but still constitutes a problem for theoretical accounts of classical conditioning framed in terms of stimulus substitution, and is still only of borderline clinical significance.

Concomitant short-term changes in the auditory evoked response, the EEG, and reaction-time performance in relation to the temporal parameters of stimulation.

Abstract.— Two experiments are described in which short‐term “habituation” of the auditory evoked response (AER) was examined using discrete trains of click stimuli and averaging across trains. In the first study, the stimuli consisted of randomly interspersed trains of regular clicks, at 3 or 10 sec interstimulus interval (ISI). In the second study, the ISIs were also short or long but were irregular varying between 2.4 and 3.6 sec in the former case and 6 to 12 sec in the latter. The N1‐P2 component of the AER diminished within the 3 sec trains especially for the regular stimulation; no such development occurred with the longer ISI. The total voltage in the background EEG and the reaction‐times to the stimuli showed essentially similar changes. The possible mechanisms governing the response decrement are discussed and it is concluded that the data may be interpreted in terms of the Groves and Thompson dual‐process theory of habituation.

Functional differentiation between late components of visual evoked potentials recorded at occiput and vertex: Effect of stimulus interval and contour

The effects of interstimulus interval (ISI) and stimulus contour on the various deflections of the occipital and vertex-recorded visual evoked potentials (VEP) were studied. The early occipital components remained practically unaltered when the ISI varied between 6 and 1.2 sec, but 0.5 sec resulted in reduced amplitudes. The late occipital negative and positive waves (latency 120–175 and 170–260 msec) were of approximately equal amplitude with 1.2 and 6 sec ISIs, but a 3 sec ISI produced an amplitude maximum which nevertheless failed to be statistically significant. On the other hand, the apparently similar vertex waves (latency 110–160 msec and 160–260 msec) declined almost linearly with decreasing ISI and this was also statistically significant ( P < 0.01 and P < 0.05 for the negative and positive component). When the flash was bounded by a rectangular contour subtending horizontally 13 and vertically 7° of visual angle, the VEPs were significantly different from responses elicited by uniform stimuli. Different behaviours were again revealed. The late negative occipital wave was reinforced when a contour was present in the stimulus whereas the vertex waves were attenuated. Ocular fixation did not seem to be involved in these effects. On the basis of these findings it is suggested that the apparently similar late VEP deflections at the occiput and vertex represent different neurophysiological phenomena.