Effects of mesencephalic reticular formation lesions on habituation of startle and lick suppression responses in the rat.

In 2 experiments with 43 male albino Holtzman rats, extensive damage to the mesencephalic reticular formation (MRF) altered long-term habituation of the acoustic startle response without disrupting short-term habituation. Ss with MRF lesions, although initially neither more nor less responsive than controls, could not attain as low a long-term asymptote of habituation as could control Ss with repeated presentations of an auditory stimulus. Changing the quality of the auditory stimulus abolished the asymptotic difference in responsiveness. With repeated presentations of the 2nd auditory stimulus, control Ss again reached a significantly lower long-term habituation asymptote than did Ss with MRF lesions. The course of long-term habituation for the 2 groups suggested a disruption of an extrinsic, inhibitory habituation process by the lesions. The effects of MRF lesions were specific to the acoustic startle response. Control Ss and those with lesions showed comparable response levels, short-term habituation, and long-term habituation of the lick suppression response. Responsiveness and habituation to tactile stimuli were comparable for the 2 groups on both lick suppression and startle response measures. (32 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Habituation of the acoustic startle response in rats after lesions in the mesencephalic reticular formation or in the inferior colliculus.

Extensive damage to the mesencephalic reticular formation (MRF) in 24 male albino rats altered long-term habituation of the acoustic startle response without disrupting short-term habituation. The MRF lesions did not alter initial startle amplitudes, but the Ss with lesions were unable to attain as low a long-term asymptote of habituation as could 21 control Ss. Subsequent manipulation of stimulus intensity and interstimulus interval revealed no differences in short-term habituation between the 2 groups. Large lesions to the inferior colliculus (IC) of 22 Ss did not disrupt long-term habituation of the acoustic startle response, but these Ss were unable to suppress responding as much as controls to intense stimuli presented rapidly. The deficits in long-term habituation following MRF lesions suggest a disruption of an extrinsic, inhibitory mechanism of habituation. The deficits following IC lesions could have been due either to a disruption of a short-term habituation mechanism or to an increase in response sensitization produced by the lesions. (30 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Influence of long-term sensitization on long-term habituation of the acoustic startle response in rats: Central gray lesions, preexposure, and extinction.

The relation between long-term decrements of the acoustic startle response in rats and the development of freezing behavior during habituation training was examined. Freezing behavior developed over the initial trials of habituation training, and the rate of long-term response decrements was found to be inversely related to the development of freezing. Manipulations (neurological or behavioral) that either reduced the level of freezing or retarded its development promoted startle response decrements. In Experiment 1, rats receiving electrolytic lesions of the ventrolateral periaqueductal gray demonstrated both accelerated long-term startle response decrements and retarded development of freezing behavior. In Experiment 2, preexposure to the startle apparatus (i.e., latent inhibition) accelerated long-term startle decrements and inhibited development of freezing. In Experiment 3, exposure to the startle apparatus following initial habituation training (i.e., extinction) reduced both freezing behavior and startle response amplitudes. The results are discussed in terms of the influence of Pavlovian fear conditioning on long-term habituation of the acoustic startle response. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Strychnine increases acoustic startle amplitude but does not alter short-term or long-term habituation.

Used the glycine antagonist strychnine (1.0 mg/kg, ip, 10 min before treatment) to investigate the involvement of glycinergic neurons in the development and/or expression of short-term (within-session) habituation (Exp I) and long-term (between-sessions) habituation (Exps II and III) of the acoustic startle response in 120 male albino Sprague-Dawley rats. Over a range of eliciting-stimulus intensities (95, 105, and 115 db) and interstimulus intervals (3, 7, 13, and 27 sec), strychnine markedly increased startle amplitude, relative to water injection, whereas it failed to attenuate the rate of within-session habituation (Exp I). In Exp II, Ss that were exposed to daily sessions of startle-eliciting stimuli for 4 days and then tested on Day 5 showed lower levels of startle amplitude than Ss with no prior habituation training. Strychnine injected prior to the test session again increased startle amplitude but did not block the expression of between-sessions habituation. In Exp III, Ss injected with either strychnine or water prior to each of 3 daily habituation training sessions and subsequently tested on Day 4 showed similar between-sessions habituation. In general, results show that strychnine increased startle amplitude without affecting either within-session or between-sessions habituation of acoustic startle. (12 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Long-term habituation to repeated loud noise is impaired by relatively short interstressor intervals in rats.

The phenomenon of spaced (longer intertrial interval) compared with massed (shorter intertrial interval) training leading to better long-term habituation and associative learning is well documented. However, the effects of intertrial intervals on response habituation to repeated stress exposures have not been previously examined. The present experiments found that massed (six 30-min exposures of 95 dB white noise in 6 hr) and spaced (one 30-min exposure daily for 6 days) noise exposures led to similar habituation of plasma corticosterone and ACTH responses, heart rate, and core body temperature after the 6th exposure in male Sprague-Dawley rats. However, these habituated responses were not retained in the massed group on a similar noise re-exposure 48 hr later, compared with the spaced group. The habituated responses found in the massed group after the 6 noise exposures were not due to differential hearing threshold shifts, as examined with modifications of the acoustic startle reflex. These data indicate that relatively short interstressor intervals impair long-term stress adaptation. This series of studies supports the idea of distinct short- and long-term habituation processes to stress responsiveness. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Contextual control of long-term habituation in rats.

This study examined contextual control of long-term habituation and whether such effects are dependent on the habituating response system. Habituation of the acoustic startle response transferred from the home cage to the testing context, whereas habituation of lick suppression was context specific (Experiments 1 and 2). Contextual control of habituation was demonstrated between 2 experimental contexts for lick suppression to a tone (Experiment 3) and bar-press suppression to a light (Experiment 4). Experiment 5 extinguished habituation of lick suppression and the orienting response to a tone with 27 exposures to the habituation context. Context specificity of both responses also was found. Previous failures to demonstrate contextual control of habituation may be due to the choice of response system and to less sensitive procedures to detect response recovery. The habituation mechanism for startle is independent from the process or processes that underlie habituation in other response systems, but the nature of these mechanisms is not yet known. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Recovery from habituation in Caenorhabditis elegans is dependent on interstimulus interval and not habituation kinetics.

The habituation of the tap withdrawal reflex of Caenorhabditis elegans was assessed to determine whether the kinetics of recovery from habituation were dependent on the interstimulus interval (ISI) uscd during habituation training or alternately, on the rate and asymptotic level of habituation produced at a given ISI. Two groups of intact animals were trained at either a 10-s (CON10) or a 60-s (CON60) ISI Laser ablation was used to alter the habituation kinetics in one further group of animals (PLM10) independent of ISI. Although the PLM10 animals trained at a 10-s ISI habituated like CON60 worms the recovery from habituation of the PLM10 animals very closely resembled the recovery of the CON10 worms. Thus recovery kinetics are dictated by consequences of a given ISI which do not impact upon habituation rate and asymptote. This suggests the recruitment of multiple ISI-dependent processes during habituation in C. elegans. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Potentiation of the acoustic startle response by a conditioned stimulus paired with acoustic startle stimulus in rats.

The hypothesis that the standard acoustic startle habituation paradigm contains the elements of Pavlovian fear conditioning was tested. In a potentiated startle response paradigm, a startle stimulus and a light conditioned stimulus (CS) were paired. A startle stimulus then was tested alone or following the CS. Freezing behavior was measured to index conditioned fear. The startle response was potentiated on CS trials, and rats froze more in CS than in non-CS periods. In Experiment 1, response to a previously habituated, weak startle stimulus was potentiated. In Experiment 2, response to the same stimulus used as the unconditioned stimulus (US) in training was potentiated. This CS-potentiated response retarded the course of response decrements over training sessions as compared with an explicitly unpaired control group. Conditioned fear is a standard feature of this habituation paradigm, serves to potentiate the startle response, and provides an associative dimension lacking in the habituation process per se. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Short-term and long-term habituation of the acoustic startle response in chronic decerebrate rats.

13 chronic decerebrate male albino rats, maintained in good condition for 31–84 postoperative days, showed significant within-session habituation of the acoustic startle response. However, they showed no habituation over days under conditions that produced significant response deficits in controls. The decerebrates' stimulus-provoked response deficits may have endured for up to 40 min between sessions, and they were apparently more than normally susceptible to stimulus-provoked sensitization. Data are consistent with models that assume that the mechanisms for short-term habituation are intrinsic to the stimulus-response (S–R) pathway in the lower brain stem. On the other hand, relatively permanent long-term habituation of the acoustic startle response must be mediated by extrinsic mechanisms rostral to the S–R pathway that superimpose an inhibitory influence on that pathway. (32 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Vestibular habituation in paralyzed cats.

Studied the role of the eye movement response in the production of vestibular habituation in 12 cats. One group of Ss was subjected to an habituation series of 15 unilateral caloric irrigations while paralyzed with gallamine triethiodide. A 2nd group underwent an identical habituation procedure but was not paralyzed. Tests conducted following recovery from paralysis showed that the responses of the previously is Ss were habituated and did not differ from the responses of Ss habituated in a normal manner. Data support a central origin for the phenomenon of vestibular habituation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Pharmacological and anatomical dissociation of two types of habituation.

Notes that both the exploration of a novel environment (an operant response) and the startle response (an elicited response) share certain functional characteristics (e.g., both response measures wane as a function of exposure and show spontaneous recovery). This commonality has led to the assumption that both measures can be used as an index of a common process of habituation. Results of the present 2 experiments with a total of 96 CFE and 10 Sprague-Dawley male albino rats show that scopolamine (but not methyl scopolamine) greatly impaired habituation of exploration but had no direct effect upon habituation of startle. Medial septal lesions impaired the rate of habituation in both cases. These differential effects imply that (a) contrary to previous conceptualizations, the 2 measures of habituation do not reflect a unitary process; and (b) anticholinergic drugs and medial septal damage do not influence the same neural substrate in terms of behavioral inhibition. (16 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Signal-to-noise ratio as a predictor of startle amplitude and habituation in the rat.

Measured the startle response in 63 male Sprague-Dawley albino rats using tones of various intensities at various levels of background noise. Tone intensity and background noise interacted in their effects on startle amplitude, but overall startle bore a nonmonotonic relationship to the signal-to-noise (S/N) ratio (tone intensity minus background noise). The inflection point of this function changed with habituation; and under some conditions habituation curves of separate groups, when presented with tones at different background-noise levels, actually crossed. Habituation was directly related to the S/N ratio in training, and S/N ratio was a better predictor of habituation than tone intensity alone or background noise alone. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Habituation of the Acoustic and the Tactile Startle Responses in Mice: Two Independent Sensory Processes.

To test whether habituation is specific to the stimulus modality, the authors analyzed cross-habituation between the tactile startle response' (TSR) and the acoustic startle response (ASR). The acoustic artifacts of airpuffs used to elicit the TSR were reduced by using a silencer and were effectively masked by background noise of 90-100 dB sound-pressure level. ASR was elicited by 14-kHz tones. TSR and ASR habituated in DBA and BALB mice: both the TSR and ASR habituated to a greater extent in DBA mice than in BALB mice. In both strains, habituation of the TSR did not generalize to the ASR, and vice versa. From this, the authors concluded that habituation of startle is located in the sensory afferent branches of the pathway. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Habituation and retention of habituation in the leech (Macrobdella decora).

Studied habituation of movement responses by 20 leeches in 2 experiments using light onset and water current as stimuli. Ss habituated to light onset and retained habituation for at least 2 successive 24-hr periods. Habituation to water current was influenced in the expected way by ITI. Ss habituated in fewer trials with a 30-sec ITI than with a 60-sec ITI. Response facilitation appeared early in habituation in both experiments and is discussed in terms of sensitization and response interference. Base rates of responding in the absence of specific eliciting stimuli were zero. Results are considered in terms of generality of processes associated with habituation and previous findings with species of annelids. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Tap withdrawal circuit interneurons require CREB for long-term habituation in Caenorhabditis elegans.

We investigated the role of the Caenorhabditis elegans CREB (cAMP response element binding protein) homologue, crh-1, in response to tap (nonlocalized mechanosensory stimulation) and tap habituation. Worms with a loss-of-function mutation in crh-1 performed smaller reversals in response to tap than did wild-type worms and did not show long-term memory for spaced training 24-hr posttraining; however, they did show short-term habituation to tap stimuli when stimuli were presented at both 10-s and 60-s interstimulus intervals, and showed 12-hr intermediate memory for spaced habituation training (intermediate-term memory). Expressing CRH-1 broadly throughout the nervous system and in a subset of interneurons of the tap withdrawal circuit, but not in the mechanosensory neurons, rescued the long-term memory defects observed in crh-1 mutants. Here we show for the first time that CREB is required for long-term habituation and show that the interneurons of the tap withdrawal response circuit are the locus of plasticity for long-term mechanosensory habituation in C. elegans. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Dishabituating long-term memory for gustatory habituation in the cabbage looper, Trichoplusia ni.

The gustatory rejection response of the cabbage looper, Trichoplusia ni (Lepidoptera: Noctuidae), habituates to antifeedant compounds, allowing for the consumption of deterrent yet nontoxic plant materials. In the present study, we demonstrate that habituation to an antifeedant compound (quinine) persists through the moult between larval instars. As an indirect test of whether the memory was protein synthesis-dependent, we tested whether disrupting protein synthesis would block memory reconsolidation after a reminder. The results indicated that disrupting protein synthesis in habituated larvae following a reminder treatment (reexposure to quinine) eliminated the memory for habituation and restored the antifeedant properties of the quinine. We then examined whether the learned memory could be dishabituated and whether this would disrupt or eliminate long-term memory. We show that 6 hr after exposure to a novel/noxious stimulus (a second antifeedent, xanthotoxin) habituated larvae showed a transient dishabituation-like effect in which the quinine deterred feeding again. However, this effect did not permanently eliminate the habituation produced by the extended exposure as larvae tested 72 hr after xanthotoxin exposure again showed a willingness to consume the quinine treated leaves, indicating that the earlier habituation was still present. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Comparison between radiation-induced cell cycle delay in lymphocytes and radiotherapy response in head and neck cancer

Two experiments examined the frequency specificity of habituation of the acoustic startle response in the rat. Following the long-term habituation of startle to one of two pure tone stimuli in Experiment 1, animals were presented with the other stimulus. Startle response asymptotes were unaffected by this change in stimulus frequency. Short-term habituation of startle also was insensitive to stimulus frequency. In Experiment 2, pure tone stimuli were used to provoke both a startle response and the interruption of drinking. Long-term habituation of startle to either stimulus was unaffected by a change in frequency. Animals that received the two stimuli on alternating days showed as rapid a habituation as did the groups receiving only one stimulus frequency during acquisition. Conversely, the lick suppression measure was found to be frequency specific. Lick suppression durations rose to pre-habituation levels when the frequency of the stimulus was changed. Animals that received the two stimuli on alternating days showed retarded habituation compared to those groups presented with only one stimulus frequency during acquisition. Although long-term habituation of startle is not stimulus specific, it is mediated by central processes and thus remains a valuable model in the study of neurophysiological mechanisms of behavioral change.     

Refractory period and habituation of acoustic startle response in rats.

Conducted 4 experiments, each with 10 male albino rats, to determine the time course of the refractory period of the acoustic startle response. The refractory effect was shown to be highly dependent upon the interval between 2 startle stimuli but independent of the intensity of the stimuli at a given interval, provided that the intensity of both stimuli was the same. A model based on summation of refractory effects to repetitive stimulation did not predict habituation to repetitive stimulation. The interaction between refractory effect and habituation was discussed, and it was suggested that short interstimulus intervals reduce the effective intensity of the habituation stimulus so that the effects of frequency and intensity become confounded in habituation studies where the interval between habituation stimuli invades the refractory period of the response being studied. (20 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Acoustic startle response and habituation in freezing and nonfreezing rats.

Divided rats according to their responses to startle-eliciting stimuli into 2 groups with different emotional states. About half of the 54 female Sprague-Dawley rats showed long-lasting freezing behavior after 1–8 stimuli (10 kHz, 110 dB spl). In freezing rats the startle amplitude was higher than in nonfreezing rats, even on the very first startle response. This finding demonstrates that the anxiety state of these animals before the 1st startle-eliciting stimulus, and not just the aversiveness of the stimulus, contributes to freezing behavior. In addition, in freezing rats there was no influence of spontaneous motor activity or of adaptation time on startle amplitude. Only in nonfreezing rats were high motor activities correlated with lowered startle amplitudes, and only in these rats did the course of startle habituation depend on adaptation time. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effect of stressor intensity on habituation and sensitization of glucocorticoid responses in rats.

Studied the effect of stressor intensity on habituation/sensitization of the adrenocortical stress response (ASR) in rats. When lower intensity shock was given, the response first habituated to no-shock control levels but later returned to the same magnitude as seen on the 1st probe day. Plasma corticosterone responses given higher intensity shock never habituated and instead demonstrated an increased response indicative of sensitization. Responsiveness to exogenous adrenocorticotropin 24 hr after the last stress session was monotonically related to the intensity of the stressor presented during the experimental sessions. Data are consistent with the rule from habituation literature that stimulus intensity is inversely related to the magnitude of habituation and extend the dual process theory of P. M. Groves and R. F. Thompson (see record 1971-02046-001) to an endocrine respondent. The data also suggest that an explanation as to the discrepancies in the literature concerning ASR to repeated presentation of stressors may relate to differences in the stressor parameters used. (PsycINFO Database Record (c) 2010 APA, all rights reserved)