Interstimulus interval effects on the habituation of the contraction response in the worm Eisenia foetida.

Presentation of auditory stimuli over interstimulus intervals (ISIs) of several minutes to sleeping rats produced significant habituation of the electroencephalographic (EEG) arousal response. The arousal response habituated to an asymptote after only two or three stimulus presentations. Little or no spontaneous recovery occurred between sessions separated by 24 or 72 hr. The habituation produced by a single stimulus presentation was retained for at least 24 hr, and orderly habituation was shown with a 24-hr ISI. Approximately 90% retention of habituation was shown 32 days following 10 stimulus presentations, and some degree of retention was shown for as long as 50 days. After habituation had reached a long-term asymptote, 600 stimulus presentations over 2-sec ISIs produced further response decrements, but these decrements recovered completely within a matter of minutes and responsiveness returned to the previously established long-term asymptote. Habituation was shown to be frequency-specific over both 24-hr and 32-day intervals. Habituation produced by stimulus presentations to awake animals transferred to the condition in which stimuli were presented to sleeping animals.

1. Neurons in nucleus laminaris (NL) of birds are the first to receive binaural information and are presumed to play a role in encoding interaural time differences (ITDs). We studied extracellular single-unit responses of NL neurons in slices of the auditory brain stem of the chick. The afferents to NL were activated by electrical stimulation of nucleus magnocellularis (NM) or the auditory nerve. Changes in responses were measured as the delay between trains of bilateral stimuli (the simulated interaural time difference or S-ITD, n = 26) was varied and as the interstimulus interval and stimulus amplitude were varied (n = 61). 2. The probability of an action potential and the action-potential latency varied as a function of interstimulus interval. Most NL neurons showed a greater response probability and a shorter response latency to an interstimulus interval between 2.5 and 3.5 ms. The interstimulus interval that produced the minimum response latency was slightly longer than the interval that produced the maximum response probability. In contrast, NM neurons (n = 4) showed no preferred rate, instead, the probability of firing increased as the interstimulus interval increased. 3. Responses to bilateral stimulation showed that NL neurons can act as coincidence detectors. NL neurons responded most reliably when activated simultaneously by their two inputs and, at favorable S-ITDs, two subthreshold inputs combined to produce an action potential. 4. NL neurons also exhibited inhibition during bilateral stimulation. At unfavorable S-ITDs a subthreshold input combined with a suprathreshold input produced fewer action potentials than evoked by the suprathreshold input alone. 5. The latency of the bilateral response varied as a function of S-ITD. At S-ITDs near coincidence the latency of the bilateral response was shorter than the latency of either of the unilateral responses. Away from coincidence, the latency of the bilateral response was largely determined by the latency of the stronger unilateral response. When the unilateral responses were of similar strength, the earlier stimulus determined the latency of the bilateral response. 6. The range of S-ITDs producing a maximal response varied as a function of stimulus strength but was never less than approximately 300 microseconds. This is greater than the maximum possible ITD of sound calculated for the chick's head size. From these data we hypothesize that, in the chick, single units cannot uniquely encode ITDs, but rather ITDs may be coded by the proportion of maximally firing cells along an isofrequency band in NL.

Predictions about the effect of interstimulus intervals (ISIs) in desensitization were made from the habituation model and tested with a series of Ss, each serving as his own control. Strong items desensitized faster with long ISIs, though weak items were not affected. No effects on long-term response decrements were found. A second experiment examined an interpretation of the stimulus-length effect in desensitization in terms of an extension of the recovery period between stimulus onsets. The results permitted rejection of the hypothesis.

Prokasy and Whaley (1961) gave 1 2 human Ss extensive training in the classical eyelid conditioning situation, where the independent variable was the set of ITIs (intertrial intervals) of 5, 10, 15, 20, 25, and 30 sec. They were interspersed in an unpredictable order over 679 uials administered in seven sessions. It was found that probability of response following the different 1TIs did not vary as a function of ITI. This result was interpreted as incompatible with the hypothesis that response-produced inhibition (Hull, 1952, p. 9) explains the superiority of spaced to massed practice obtained in earlier classical eyelid conditioning studies (e.g., Spence & Norris, 1950; Prokasy, Granc, & Myers, 1958) . It was the purpose to test other implications of the response-produced inhibition hypothesis. Specifically, if inhibition is assumed to cumulate with massed trials, then a later switch to spaced trials should result in an increase in response probability. Similarly, after training with relatively spaced trials, a shift to massed trials should result ic, a decrement in response probability. PROCEDURE The apparatus is described in Prokasy and Whaley ( 1 9 6 1 ) . The CS was a brightness change of 3.8 to 190 mL. lasting 500 msec. The UCS, a 50-msec. puff of nitrogen, was delivered to the right cornea from .75 in., and was of sufficient intensity to support a 210-mm. column of mercury. The interstimulus interval was 500 msec. Ss were 27 male students between the ages of 18 and 22, who received course credit in introductory psychology for volunteering. One was terminated due to failure to condition; 2 failed to complete the training sessions because of end-of-semester scheduling problems. Two IT1 ranges were selected: a massed range including ITIs of 5, 10, 15, and 2 0 sec., and a spaced range including ITIs of 20, 25, 30, and 35 sec. The 24 Ss were assigned at random to two groups. Group MS received 5 sessions of 65 trials each with the massed IT1 range followed by 5 sessions of 65 trials each with the spaced IT1 range. Group SM received the spaced range for the initial 5 sessions and the massed range for the final 5 sessions. In all sessions, with both ranges, the 4 lTIs were administered in a pre-determined, unpredictable order, with the resrrlcuon that each IT1 appear 1 6 times in each session and that no one IT1 follow itself more than once. Thus, across the 10 sessions Ss in Group MS received each of the 4 massed ITIs 8 0 times each, followed by each of the 4 spaced ITIs 8 0 times each. Ss in Group SM received the same treaunent except that the 5 spaced sessions preceded the 5 massed sessions. Instructions were read S ac the beginning of Session 1. S was given neutral instructions which indicated that he should not try to control his responses in any way and that he should keep the CS panel in view at all times. In subsequent sessions Ss were reminded of instructions informally. Although it was not possible to run Ss on 1 0 consecutive days, rarely was there a break between sessions of longer than 3 days.

To begin an investigation of the cellular processes that underlie long-term memory in the nematodeCaenorhabditis elegans, it is first necessary to determine thatC. elegans is capable of retention over 24 h, and to investigate the factors that may influence the expression of long-term memory. In the present study, the effects of stimuli number, interstimulus interval (ISI), and training procedure on long-term retention of habituation were tested inC. elegans. At a long (60-sec) ISI, distributed training sessions produced long-term habituation retained for 24 h, whereas massed training sessions or training with few stimuli did not. When training was performed at a short (10-sec) ISI, long-term habituation was not detectable with testing at either a 10- or a 60-sec ISI. The long-term habituation observed after distributed training sessions at a 60-sec ISI was consistently expressed when the training procedures were varied. Thus it is clear thatC. elegans can reliably express long-term retention for distributed training sessions at a 60-sec ISI, making the system a candidate for further investigations into the cellular processes supporting memory.

Three levels (.5, 1.0, and 2.0 sec) of interstimulus interval (ISI) and presence vs absence of a masking task were manipulated in a human eyelid reflex conditioning situation. Through the use of a two-phase model of conditioning performance, it was concluded that (1) increasing the ISI and introducing a masking task increased the duration of Phase 1, (2) as ISI increased, the amount of conditioning decreased, (3) the trial-by-trial rate of change in response probability increased as a function of ISI, and (4) the masking task reduced operator limits. It was also noted that the typical ISI function is composed of rate effects at short ISis and conditioning limit effects at long ISIs and that the larger 0 at larger ISis does not follow from a model of the stimulus trace hypothesis.

Promoting endogenous associative plasticity in human primary motor cortex

Summary The effects of light stimulation interpolated during a rest interval were studied in a three-phase investigation of retention of habituation of the contraction response to air puff in the earthworm, L. terrestris (N = 48). Worms were assigned 16 per group to three conditions (zero, 24, or 48 air puffs) in Phase 1; half were given five stimulations of white light, and the others rested in Phase 2; in Phase 3 all animals received air puffs to habituation criterion. Results showed that original habituation with air puff decreased responses to light, and habituation with light decreased responses to air puff in Phase 3. Thus evidence indicated intermodal stimulus generalization of habituation, but not dishabituation.

When two-frame apparent motion stimuli are presented with an appropriate inter-stimulus interval (ISI), motion is perceived in the direction opposite to the actual image shift. Herein, we measured a simple eye movement, ocular following responses (OFRs), in macaque monkeys to examine the ISI reversal effect on oculomotor. Two-frame movies with an ISI induced reversed OFRs. Without ISI, the OFRs to the two-frame movie were induced in the direction of the stimulus shift. However, with ISIs ≥10ms, OFRs in the direction opposite to the phase shift were observed. This directional reversal persisted for ISIs up to 160ms; for longer ISIs virtually no ocular response was observed. Furthermore, longer exposure to the initial image (Motion onset delay: MOD) reduced OFRs. We show that these dependences on ISIs/MODs can be explained by the motion energy model. Furthermore, we examined the dependence on ISI reversal using various spatial frequencies. To account for our findings, the optimal frequency of the temporal filters of the energy model must decrease between 0.5 and 1cycles/°, suggesting that there are at least two channels with different temporal characteristics. These results are consistent with those from humans, suggesting that the temporal filters embedded in human and macaque visual systems are similar. Thus, the macaque monkey is a good animal model for the early visual processing of humans to understand the neural substrates underlying the visual motion detectors that elicit OFRs.

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

Delay eye-blink conditioning is an associative learning task that can be utilized to probe the functional integrity of the cerebellum and related neural circuits. Typically, a single interstimulus interval (ISI) is utilized, and the amplitude of the conditioned response (CR) is the primary dependent variable. To study the timing of the CR, an ISI shift can be introduced (e.g., shifting the ISI from 350 to 850ms). In each phase, a conditioned stimulus (e.g., a 400- or 900-ms tone) coterminates with a 50-ms corneal air puff unconditioned stimulus. The ability of a subject to adjust the CR to the changing ISI constitutes a critical timing shift. The feasibility of this procedure was examined in healthy human participants (N = 58) using a bidirectional ISI shift procedure while cortical event-related brain potentials were measured. CR acquisition was faster and the responses better timed when a short ISI was used. After the ISI shift, additional training was necessary to allow asymptotic responding at the new ISI. Interestingly, auditory event-related potentials to the CR were not associated with conditioning measures at either ISI.

The “novelty response” in an electric fish: response properties and habituation

A decrement in the probability of eliciting a response is observed during the course of repetitive stimulation in many response systems of both metazoa and protozoa. Those forms of metazoan response decrement called habituation have recently been characterized behaviorally. In the studies reported here, the response decrement of the contractile protozoan, Stentor coeruleus, to repeated mechanical stimulation was systemically characterized to provide a comparison with metazoan habituation. This change in response probability was closely approximated by a negative exponential function after the first few stimuli. Animals responded to parametric variations of stimulus amplitude, interstimulus interval and retention period in a manner paralleling that observed in metazoa. However, neither interpolated large amplitude mechanical stimuli nor suprathreshold electrical stimuli produced dishabituation in Stentor though these stimuli are among the most effective dishabituating stimuli for metazoan tactile response systems. Behavioral analysis of the response decrement proceeded on the assumption that Stentor contains receptor and effector mechanisms only. Since the response decrement was not correlated with a change in responsiveness to electrical stimuli, the ability of the animal to contract appears to be unaltered by the process producing the response decrement. On the other hand, weak mechanical prestimuli were found to increase the rate of the response decrement which suggests that a process of receptor adaption is operative.

Brain Response to Visceral Aversive Conditioning: A Functional Magnetic Resonance Imaging Study

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.