The role of the cerebellum in classical conditioning of discrete behavioral responses.

The cerebellum and its associated circuitry constitutes the entire essential neuronal system for classical conditioning of eye-blink and other discrete responses (e.g. limb flexion) learned with an aversive unconditioned stimulus (US) using the standard delay paradigm where the conditioned stimulus (CS) and the US coterminate. Evidence reviewed here strongly supports the following conclusions. The CS pathway involves sensory relay nuclei projections to the pontine nuclei and its mossy fiber projections to the cerebellar cortex and nuclei. The US pathway involves activation of the inferior olive (dorsal accessory olive for eye blink) and its climbing fiber projections to the cerebellar cortex and nuclei. The conditioned response (CR) pathway involves the cerebellar interpositus nucleus, the superior cerebellar peduncle pathway to the magnocellular red nucleus and rubral projections to premotor and motor nuclei generating the behavioral response. Anatomical data, neuronal unit recordings, electrical stimulation, lesions and methods of reversible inactivation all strongly support the hypothesis that the essential memory trace for the learning of these discrete conditioned responses is formed and stored in the cerebellar interpositus nucleus. Neuronal/synaptic plasticity is also established in the cerebellar cortex in this form of learning but the role of the cortex is less clear. We argue that the cortex plays a key role in normal acquisition and adaptive timing of the conditioned response, under certain circumstances, but it remains unclear exactly what features of conditioning are being encoded in the cerebellar cortex in this basic form of associative learning and memory.

Eyeblink conditioning deficits indicate timing and cerebellar abnormalities in schizophrenia.

Accumulating evidence indicates that individuals with schizophrenia manifest abnormalities in structures (cerebellum and basal ganglia) and neurotransmitter systems (dopamine) linked to internal-timing processes. A single-cue tone delay eyeblink conditioning paradigm comprised of 100 learning and 50 extinction trials was used to examine cerebellar timing circuits in 13 medicated patients with schizophrenia and 13 age- and sex-matched controls. Patients with schizophrenia showed impaired learning of the conditioned response compared to controls and also greater within-subject variability in the timing of their responses. These findings are consistent with models of schizophrenia in which timing deficits underlie information-processing abnormalities and clinical features of the disorder.

Comparison of single unit responses to tone, light, and compound conditioned stimuli during rabbit classical eyeblink conditioning.

Unit recordings and lesion studies have implicated the cerebellum as an essential site for the acquisition and maintenance of the conditioned eyeblink response. The current study looked at the neural characteristics of conditioned stimulus (CS) processing in the interpositus nucleus of the cerebellum after training New Zealand white rabbits (Oryctolagus cuniculus) in one of two conditioning paradigms: (a) compound conditioning (CMP), a compound CS consisting of light and tone paired with an air puff unconditioned stimulus (US); or (b) stimulus compounding (ALT), alternating blocks of tone CS and light CS trials paired with the air puff US. Single unit responses were recorded during five sessions after the animals had reached an asymptotic level of responding. Animals were tested for behavioral and neural responses to CS alone trials that included tone alone, light alone, and compound tone-light trials. For the CMP group, the compound CS elicited 80 to 90% conditioned eyeblink responses (CRs), whereas the individual tone and light CSs elicited only 40 to 50% CRs. For the ALT group, all three CSs (tone, light, and compound) elicited very high levels of responding of at least 80% CRs. For the CMP group, there were roughly equal numbers of cells responding to all of the CSs. This includes cells that responded exclusively to one, and only one, of the three stimuli and also those cells that responded to combinations of two or more. Cells from the ALT group were far more likely to respond exclusively to only one of the CSs. Both the behavioral and physiological results suggest that the compound tone-light stimulus was processed as a distinct stimulus, separate from the component tone and light. These results are discussed in the context of multisensory processing.

P300, disinhibited personality, and early-onset alcohol problems.

BACKGROUND: Recent research suggests that a reduced P300 amplitude of the event-related potential is associated with a vulnerability to alcoholism. This study tested the hypothesis that reductions in the P300 amplitude would be associated with specific dimensions of disinhibited personality (social deviance proneness and impulsivity) and that these personality traits would mediate the association between P300 and alcohol problems in a young adult sample that varied widely in disinhibitory traits. METHODS: Alcohol problems, personality (impulsivity, social deviance, harm avoidance, and excitement seeking), and event-related potentials were measured in a sample of 190 subjects (87 men, 103 women) with a mean age of 20.7 +/- 1.9 years. RESULTS: Social deviance, impulsivity, and alcohol problems were associated with reductions in the P300, but only in male subjects. A structural model suggested that social deviance, impulsivity, and alcohol problems were all strongly related to P300 amplitude at Fz. Further analyses indicated that for male subjects, social deviance mediated the association between P300 at Fz and alcohol problems as well as the association between impulsivity and alcohol problems. CONCLUSIONS: This study suggests that reduced P300s are strongly associated with a general tendency toward antisocial, defiant, and impulsive traits, which might, in turn, increase the risk for alcohol abuse. The lack of an association between reduced P300s and personality or alcohol problems in women was unexpected and deserves further study.

Constraint, alcoholism, and electrodermal response in aversive classical conditioning and mismatch novelty paradigms.

This study investigated whether low levels of the personality trait of constraint and early-onset alcoholism would be associated with deficits in aversive conditioning and smaller responses to novelty in a stimulus mismatch protocol. Personality traits (constraint and socialization) and skin conductance responses (SCRs) during conditioning and novelty paradigms were assessed in alcoholics (n=41) and non-alcoholics (n = 32). The conditioning protocol involved measuring SCRs after conditioned stimuli (CS+: tones) paired with shock, CS- tones unpaired with shock, and CS+ probes unpaired with shock. The mismatch protocol involved measuring SCRs to auditory stimuli consisting of a series of 5 pure tones of the same pitch followed a shorter white noise stimulus (the novel stimulus). Contrary to the hypothesis, alcoholics did not differ from non-alcoholics in SCRs to CS+ probes or on the mismatch measure (SCR novel tone-SCR to 5th tone). Higher levels of constraint and self-reports of fear during conditioning were associated with smaller responses to both the CS+ probes and the CS- tones as well as the mismatch measure within non-alcoholics, but not within alcoholics. In alcoholics, low constraint was associated with greater habituation to CS+ probes, and poor differential conditioning on measures of change across trials in SCR to CS+ probes and CS- stimuli. The results suggest that different processes influence levels of constraint in non-alcoholics and alcoholics. The data indicate that low constraint in non-alcoholics is associated with allocating fewer processing resources to potentially significant stimuli, rather than being associated with a specific deficit in aversive conditioning per se.

Discrimination reversal conditioning of an eyeblink response is impaired by NMDA receptor blockade.

In the present study we examined the effects of the specific NMDA receptor antagonist CPP on discrimination reversal learning in rabbits. We report two primary findings. First, the institution of NMDA receptor blockade had no effect on a learned discrimination. Second, after stimulus reversal, CPP treatment impaired acquisition of the discrimination reversal. This impairment manifested itself early in training as a retardation in acquisition of a CR to the new CS+ and late in training as an inability to suppress responsiveness to the new CS-. Given the comparability of the present results with previously published results for phenytoin-treated rabbits, we suggest that the effects of phenytoin on learning in this paradigm is at least in part mediated by its effects on NMDA receptors. We further suggest that these findings emphasize the need to better define the role of NMDA receptor activation and hippocampally-mediated circuits in a variety of associative learning paradigms.

Learning-related interpositus activity is conserved across species as studied during eyeblink conditioning in the rat.

Single-unit activity was monitored in the interpositus nucleus of the cerebellum during standard delay conditioning of the eyeblink response in freely-moving rats. The rats were implanted with recording electrodes in the interpositus nucleus then received paired presentations of a tone-conditioned stimulus (CS) and eye-shock unconditioned stimulus during acquisition training. The acquisition training was followed by CS-alone extinction training. Learning-related activity in the interpositus nucleus developed over the course of acquisition training and then activity returned to baseline levels during subsequent extinction training. These findings are consistent with rabbit studies that have demonstrated similar changes in neuronal activity in the interpositus nucleus over the course of acquisition and extinction of the eyeblink response, thus providing strong evidence for the generality of the neural substrates of eyeblink conditioning across species.

Rabbit classical eyeblink conditioning is altered by brief cerebellar cortical stimulation.

A pair of studies examined how cortical intracerebellar stimulation (ICS) affects eyeblink conditioning in the rabbit. Rabbits were implanted with chronic bipolar stimulating electrodes in the cell body layers of cerebellar lobule H-VI. Brief (40 ms) trains of intracranial stimulation (100 Hz, 250 microA) were delivered during training trials [forward pairings of a tone-conditioned stimulus (CS) with an air puff unconditioned stimulus (US)]. In Experiment 1, the onset of ICS varied randomly within sessions. US-onset-coincident ICS proved detrimental to the maintenance of conditioning [measured as the percentage of trials on which conditioned responses (CRs) were made] compared to ICS that ended 60 ms before US onset. Based on these findings, a second experiment compared a group trained with ICS consistently delivered at US onset to groups trained with ICS consistently delivered either at CS onset or between the two stimuli, as well as to unstimulated control subjects. Animals receiving CS- or US-coincident ICS learned slowest, whereas animals receiving middle stimulation learned more quickly than all other groups. In both Experiments 1 and 2, highly trained animals produced blinks in direct response to the stimulation. These data are discussed in terms of a new hypothesis concerning interactions between cerebellar cortex and the deep cerebellar nuclei during eyeblink conditioning--a rebound from inhibition hypothesis.

Classical eyeblink conditioning: clinical models and applications.

In this paper, we argue that the main reason that classical eyeblink conditioning has proven so useful when applied to clinical situations, is that a great deal of information is known about the behavioral and neural correlates of this form of associative learning. Presented here is a summary of three lines of research that have used classical eyeblink conditioning to study three different clinical conditions; autism, fetal alcohol syndrome, and obsessive-compulsive disorder. While seemingly very different clinical conditions, classical eyeblink conditioning has proven very useful for advancing our understanding of these clinical pathologies and the neural conditions that may underlie them.

Evaluation of behavioral disinhibition in P/NP and HAD1/LAD1 rats.

1. Two lines of rats specifically bred for alcohol preference were exposed to two different behavioral tasks that required behavioral inhibition to successfully solve. 2. Learning and performance of a step-down passive avoidance task and a differential reinforcement of low-rate responding task were studied in P/NP and HAD1/LAD1 rats. 3. While the P rats had difficulty in learning both tasks, HAD1, LAD1 and NP rats performed at control levels. 4. These data suggest that P rats, but not HAD1 rats, may have problems learning tasks that require inhibition of ongoing or previously learned behaviors.

The influence of traits of disinhibition on the association between alcohol use and risky sexual behavior.

BACKGROUND: Past research has demonstrated a link between alcohol use and risky sexual behavior; the processes that may underlie this association remain largely unexplored, however. Recent studies suggest that personality traits such as excitement seeking, impulsivity, and social deviance proneness may play an important role in both behaviors. METHODS: A structural model of the association between disinhibited personality traits, alcohol use, and risky sexual behavior (sex with strangers/one-night stands) was tested. We recruited a sample of 410 college students that reported a wide range of scores on self-reported measures of disinhibition. We hypothesized that disinhibited personality characteristics would be primarily responsible for the association between risky sexual behavior and alcohol problems. A third-variable model was proposed to demonstrate this association. RESULTS: The results suggested that the relationship between alcohol use and risky sexual behavior is best explained by their common association with excitement seeking. There was a significant correlation between alcohol use and risky sexual behavior when considered alone. However, when controlling for the effects of personality, the correlation was nonsignificant. In a final model, both excitement seeking and social deviance proneness were found to be significantly associated with alcohol use, and excitement seeking was significantly related to risky sexual behavior. CONCLUSIONS: Results suggest the relationship between alcohol use and risky sexual behavior is best characterized by a common association with excitement seeking.

Decision-making biases, antisocial personality, and early-onset alcoholism.

BACKGROUND: Disinhibited, antisocial traits increase the risk for early-onset alcoholism. Research also suggests that decision biases which favor immediate large rewards regardless of long-term consequences may be important mechanisms associated with the biological substrates of antisocial traits. This study tested the hypothesis that early-onset alcoholism with antisocial personality (ASP) would be associated with favoring immediate larger rewards despite their being associated with long-term losses. METHODS: Twenty-seven early-onset alcoholics with and without a diagnosis of ASP, eight subjects with ASP but no alcohol dependence, and 32 controls were tested on a task that manipulated the magnitude of immediate rewards and the magnitude of long-term punishments. The sample was recruited from the community via advertisements. RESULTS: Compared with subjects without ASP, subjects with ASP favored larger immediate rewards despite long-term losses regardless of alcohol dependence; however, they learned to shift their decisions in a more advantageous direction over time. A disadvantageous decision bias also was associated with drinking greater quantities of alcohol and having a lower IQ. CONCLUSIONS: This study suggests that ASP in a young adult noninstitutionalized sample was associated with a pattern of disadvantageous decision making similar to that observed in patients with antisocial behavioral characteristics associated with lesions in the ventromedial frontal cortex. The data also suggest that this pattern of disadvantageous decision making is associated with consuming larger quantities of alcohol but not consuming alcohol more frequently.

Impairment in eyeblink classical conditioning in adult rats exposed to ethanol as neonates.

BACKGROUND: Eyeblink classical conditioning is a learning task that engages well-defined neural circuitry in the cerebellum and brainstem. Binge-like exposure to alcohol during the neonatal brain growth spurt in rats produces neurotoxic effects on both the cerebellum and the brainstem. The precise localization of the neural substrates of eyeblink conditioning makes it an ideal task to study functional disruptions in the cerebellum and brainstem caused by early exposure to alcohol. The purpose of this study was to determine whether impairments in eyeblink conditioning caused by neonatal binge exposure to alcohol persist into adulthood, indicative of long-lasting abnormalities in cerebellar and brainstem function. METHODS: Group Ethanol received alcohol doses of 5.25 g/kg/day via intragastric intubation on postnatal days 4-9. Group Sham Intubated underwent the intragastric intubation procedures on postnatal days 4-9 but did not receive any infusions. Group Nonintubated did not receive any intubations. When all rats were at least 3 months old, they were tested in either paired or unpaired eyeblink conditioning. RESULTS: Group Ethanol showed impaired eyeblink conditioning and some abnormalities in conditioned response timing. Control groups did not differ from each other. CONCLUSIONS: The present data indicate that early exposure to alcohol has long-term effects on eyeblink conditioning, perhaps through enduring effects associated with alcohol-induced loss of Purkinje cells of the cerebellum.

Brain substrates of classical eyeblink conditioning: a highly localized but also distributed system.

The rabbit classical nictitating membrane/eyeblink conditioning preparation has proven highly valuable for delineating neural structures and systems involved in associative learning. Research conducted over the last 20 years has revealed that the essential neural circuitry for acquisition and performance of this simple, learned, motor response resides in the cerebellum and related brain stem structures. While this system appears to be highly localized, many other brain areas are recruited during eyeblink conditioning. Further, involvement of the cerebellum in associative learning and memory seems to be limited by certain parametric conditions present at the time of learning. These data suggest that classical eyeblink conditioning can also be characterized as a distributed system. Data in support of the highly localized, yet distributed nature of the neural systems involved in classical eyeblink conditioning are presented and discussed here.

Microinfusion of protein kinase inhibitor H7 into the cerebellum impairs the acquisition but not the retention of classical eyeblink conditioning in rabbits.

Rabbits were infused with H7, a general protein kinase inhibitor, into the region of the cerebellar interpositus nucleus during classical eyeblink conditioning. Acquisition of the conditioned eyeblink response was delayed by the H7 infusion, but the protein kinase inhibitor had no effect on performance of the learned response when infused after asymptotic learning had been reached. These data indicate that protein kinases in the cerebellum are involved in plasticity processes that underlie the learning of this simple conditioned behavior.

A characterization of approach and avoidance learning in high-alcohol-drinking (HAD) and low-alcohol-drinking (LAD) rats.

BACKGROUND: This study was undertaken as one of a series of experiments designed to examine basic behavioral characteristics present in rats bred specifically for alcohol preference. The basic premise for these experiments has been the idea that alcohol-preferring and -nonpreferring rats may differ in basic activation and inhibition control mechanisms that govern behavior and that different lines of alcohol-preferring rats may demonstrate differential deficits in behavioral activation and behavioral inhibition tendencies. In the present experiment, conditioned approach and avoidance behaviors were studied in alcohol-naïve high-alcohol-drinking (HAD), low-alcohol-drinking (LAD), and N/NIH rats to evaluate behavioral activation in this line of rats. METHODS: High alcohol drinking (HAD1), low alcohol drinking (LAD1), and N/Nih stock rats were trained to press a response bar during a tone signal to avoid a mild foot shock or receive a food reward. In addition, HAD2 and LAD2 rats, independently-bred replicate lines of the HAD1/LAD1 rats, were trained on the avoidance task. RESULTS: Although the HAD1 rats easily learned the appetitive version of the bar-pressing task, they did not learn the avoidance response. The LAD1 and N/Nih rats learned both the approach and the avoidance tasks normally. Similar to HAD1 rats, the HAD2 rats did not learn the avoidance response whereas LAD2 rats showed significant avoidance performance levels. CONCLUSIONS: The present data demonstrated that both HAD1 and HAD2 rats had a rather specific behavioral activation deficit: although they easily learned to press a bar to receive food reinforcement, they did not learn to press the bar to avoid a foot shock. We speculate that this failure to learn the avoidance response may be related to heightened anxiety in the HAD rats and that this excessive anxiety may lead to the development of high levels of alcohol consumption in these selectively bred rats.

Intra-cerebellar infusion of NMDA receptor antagonist AP5 disrupts classical eyeblink conditioning in rabbits.

Rabbits were infused with AP5, an NMDA receptor antagonist, into the region of the cerebellar interpositus nucleus during classical eyeblink conditioning with a tone conditioned stimulus and an air puff unconditioned stimulus. Acquisition of the conditioned eyeblink response was delayed in rabbits infused with AP5 but the NMDA receptor antagonist had little effect on conditioned responses when these same rabbits were infused a second time after reaching asymptotic responding levels. Some rabbits that received AP5 infusions for the first time after the conditioned response was well learned showed temporary alterations in response timing. These data indicate that NMDA receptor activity is involved in the acquisition of classically conditioned eyeblink response and may also be involved in regulating cellular processes involved in response timing and other aspects of conditioned response execution.

Working memory, executive processes and the effects of alcohol on Go/No-Go learning: testing a model of behavioral regulation and impulsivity.

RATIONALE: Impulsivity is associated with increased risk for alcoholism. Alcohol also may increase impulsive behavior, although little is known about the processes underlying this effect. OBJECTIVES: This study tested a model proposing that the executive processes of working memory (WM) and conditional associative learning (CAL) modulate behavioral inhibition. Subjects had either a positive (FHP) or a negative (FHN) family history of alcoholism. Hypotheses were that alcohol would increase Go/No-Go impulsive responding but only in subjects with low working memory capacity (low-WM), low-CAL ability, or FHP for alcoholism. The model also predicted that WM and CAL modulate inhibitory responses to contingency reversal on a Go/No-Go task. METHODS: A Go/No-Go learning task with a midway contingency reversal was administered to 71 FHP and 78 FHN subjects when sober and after drinking one of two moderate doses of alcohol. WM (digits backward) and CAL (conditional spatial association task) were also assessed when sober. RESULTS: Alcohol resulted in more false alarms but only in low-WM subjects. Both WM and CAL modulated learning to inhibit behavior after contingency reversal, suggesting separate modulation mechanisms for WM and CAL. Subjects with low- capacity WM and subjects with low-capacity CAL ability had more difficulty learning response inhibition after contingency reversal. FHPs and FHNs did not differ in their response to alcohol. CONCLUSIONS: The results support our model of the modulatory role of WM and CAL in the ongoing regulation of behavioral inhibitory systems. The results also suggest that individuals with low capacity WM are more susceptible to alcohol's effect of increasing impulsive behavior, suggesting that alcohol reduces the capacity of working memory to modulate response inhibition.

The effects of phenytoin on instrumental appetitive-to-aversive transfer in rats.

Antiepileptic medications are the primary treatment for seizure conditions. Over the past several years, it has become clear that the medications themselves may contribute to the negative cognitive side effects that people with epilepsy often report. In the experiments reported here, the effects of phenytoin treatment have been evaluated in rats performing an instrumental appetitive-to-aversive transfer task. We find that rats treated with phenytoin fail to acquire the avoidance response when transferred from an appetitive to an aversive context. This deficit is not due to any sensory or motor slowing resulting from the drug, nor is it a deficit that is specific to learning in an aversive context. Rather, we suggest that the deficits shown by phenytoin-treated rats in the appetitive-to-aversive transfer reflect a fundamental inability in altering the associations that were formed during the initial appetitive training.

Genetic influences on human conditionability: a twin study of the conditioned eyeblink response.

Acquisition of the classically conditioned eyeblink response is generally regarded as one of the most basic forms of associative learning. A great deal is known about how the brain encodes this simple form of learning, so that performance of this task may be an indirect indicator of brain functioning. Individual differences in response acquisition have been revealed, but largely ignored, in the research literature. We tested the temporal stability and familial origins of these individual differences using a classic twin study design. Results reveal substantial individual differences in acquisition of the conditioned eyeblink response. These differences are stable across brief retest, and differences in response acquisition exhibit familial aggregation, apparently due, in part, to genetic resemblance.