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

Eye-blink conditioning deficits indicate temporal processing abnormalities in schizophrenia

Theoretical models suggest that symptoms of schizophrenia may be due to a dysfunctional modulatory system associated with the cerebellum. Although it has long been known that the cerebellum plays a critical role in associative learning and motor timing, recent evidence suggests that it also plays a role in nonmotor psychological processes. Indeed, cerebellar anomalies in schizophrenia have been linked to cognitive dysfunction and poor long-term outcome. To test the hypothesis that schizophrenia is associated with cerebellar dysfunction, cerebellar-dependent, delay eye-blink conditioning was examined in 62 individuals with schizophrenia and 62 age-matched non-psychiatric comparison subjects. The conditioned stimulus was a 400 ms tone, which co-terminated with a 50 ms unconditioned stimulus air puff. A subset of participants (25 with schizophrenia and 29 controls) also completed the Wechsler Abbreviated Scale of Intelligence. Participants with schizophrenia exhibited lower rates of eye-blink conditioning, including earlier (less adaptively timed) conditioned response latencies. Cognitive functioning was correlated with the rate of conditioned responsing in the non-psychiatric comparison subjects but not among those with schizophrenia, and the magnitude of these correlations significantly differed between groups. These findings are consistent with models of schizophrenia in which disruptions within the cortico-cerebellar-thalamic-cortical (CCTC) brain circuit are postulated to underlie the cognitive fragmentation that characterizes the disorder.

Associative and non-associative blinking in classically conditioned adult rats

Over the last several years, a growing number of investigators have begun using the rat in classical eyeblink conditioning experiments, yet relatively few parametric studies have been done to examine the nature of conditioning in this species. We report here a parametric analysis of classical eyeblink conditioning in the adult rat using two conditioned stimulus (CS) modalities (light or tone) and three interstimulus intervals (ISI; 280, 580, or 880 ms). Rats trained at the shortest ISI generated the highest percentage of conditioned eyeblink responses (CRs) by the end of training. At the two longer ISIs, rats trained with the tone CS produced unusually high CR percentages over the first few acquisition sessions, relative to rats trained with the light CS. Experiment 2 assessed non-associative blink rates in response to presentations of the light or tone, in the absence of the US, at the same ISI durations used in paired conditioning. Significantly more blinks occurred with longer than shorter duration lights or tones. A higher blink rate was also recorded at all three durations during the early tone-alone sessions. The results suggest that early in classical eyeblink conditioning, rats trained with a tone CS may emit a high number of non-associative blinks, thereby inflating the CR frequency reported at this stage of training.

Eyeblink conditioning anomalies in bipolar disorder suggest cerebellar dysfunction

OBJECTIVES

Accumulating research implicates the cerebellum in non-motor psychological processes and psychiatric diseases, including bipolar disorder (BD). Despite recent evidence that cerebellar lesions have been documented to trigger bipolar-like symptoms, few studies have directly examined the functional integrity of the cerebellum in those afflicted with BD.

METHODS

Using a single-cue delay eyeblink conditioning procedure, the functional integrity of the cerebellum was examined in 28 individuals with BD (9 manic, 8 mixed, and 11 euthymic) and 28 age-matched healthy controls.

RESULTS

Analysis of the bipolar group as a whole indicated a conditioned response acquisition and timing deficit compared to controls. However, when the bipolar group was categorized according to mood state (mixed, manic, euthymic), individuals tested during mixed episodes were strikingly impaired, performing significantly worse than all other groups on both the acquisition and timing of conditioned responses.

CONCLUSIONS

These findings extend prior research implicating cerebellar functional abnormalities in BD and suggest that cerebellar dysfunction may be associated with mood state and course of illness.

Hippocampal response patterns during discriminative eyeblink/jaw movement conditioning in the rabbit

Rabbits were given concurrent training in eyeblink (EB) and jaw movement (JM) conditioning in which 1 tone predicted an airpuff and another tone predicted water. After 10 days of discrimination training, the animals were given 10 days of reversal training. In the discrimination phase, acquisition of the 2 conditioned responses was not significantly different; however JM discrimination errors were much more frequent than were EB errors. In the reversal phase, correct performance on EB trials increased gradually, as was expected, whereas there was immediate behavioral reversal on JM trials. Differences in size and topography of dorsal CA1 multiple-unit responses reflected the ability of the hippocampus to discriminate between stimuli in trained animals, corresponding to the performance of the behavioral discrimination. During JM trials, the rhythmicity of the neural response was further modulated by the type of the prior trial, suggesting the coding of sequential events by the hippocampus. Thus, hippocampal conditioned activity can rapidly change its magnitude and pattern depending on the specific trial type during a concurrent EB/JM discrimination task and its reversal. (PsycINFO Database Record (c) 2008 APA, all rights reserved).

Docosahexaenoic acid and cognitive function: Is the link mediated by the autonomic nervous system?

Docosahexaenoic acid is a long-chain polyunsaturated fatty acid that is found in large quantity in the brain and which has repeatedly been observed to be related in positive ways to both cognitive function and cardiovascular health. The mechanisms through which docosahexaenoic acid affects cognition are not well understood, but in this article, we propose a hypothesis that integrates the positive effects of docosahexaenoic acid in the cognitive and cardiovascular realms through the autonomic nervous system. The autonomic nervous system is known to regulate vital functions such as heart rate and respiration, and has also been linked to basic cognitive components related to arousal and attention. We review the literature from this perspective, and delineate the predictions generated by the hypothesis. In addition, we provide new data showing a link between docosahexaenoic acid and fetal heart rate that is consistent with the hypothesis.

Cannabis use disrupts eyeblink conditioning: evidence for cannabinoid modulation of cerebellar-dependent learning

While the cerebellum contains the highest density of cannabinoid receptor (CB1) in the brain, no studies have assessed the effect of exogenous cannabinoids on cerebellar-dependent learning in humans. The current study, therefore, examined the effect of chronic cannabis use on classical eyeblink conditioning (EBC), a cerebellar-mediated task which has been shown to be disrupted in CB1 knockout mice. Chronic cannabis users (24 h abstinence before study; positive THC urine drug test) free of DSM-IV Axis-I or -II disorders, were evaluated. A delay EBC task was utilized, in which a conditioned stimulus (CS; 400 ms tone) co-terminated with a corneal air puff unconditioned stimulus (US; 50 ms), thus eliciting a conditioned blink response (CR). The cannabis group exhibited markedly fewer, and more poorly timed CRs as compared to drug-naive controls. There were no differences between the groups in either the unconditioned response (UR) or an EEG measure of selective attention to the CS (N100 auditory ERP), indicating that the disruption observed in the cannabis group was specific to CR acquisition. These results suggest that cannabis use is associated with functional deficits in the cerebellar circuitry underlying EBC, a finding which corroborates the recent work in CB1 knockout mice.

Extinction of a classically conditioned response: red nucleus and interpositus

It is well established that the cerebellum and its associated circuitry are essential for classical conditioning of the eyeblink response and other discrete motor responses (e.g., limb flexion, head turn, etc.) learned with an aversive unconditioned stimulus. However, brain mechanisms underlying extinction of these responses are still relatively unclear. Behavioral studies have demonstrated extinction to be an active learning process distinct from acquisition. Accordingly, this current understanding of extinction has guided neural studies that have tried to identify possible brain structures that could support this new learning. However, whether extinction engages the same brain sites necessary for acquisition is not yet clear. This poses an overriding problem for understanding brain mechanisms necessary for extinction because such analysis cannot be done without first identifying brain sites and pathways involved in this phenomenon. Equally elusive is the validity of a behavioral theory of extinction that can account for the properties of extinction. In this study, we looked at the involvement of the interpositus and the red nucleus in extinction. Results show that, although inactivation of both nuclei blocks response expression, only inactivation of the interpositus has a detrimental effect on extinction. Moreover, this detrimental effect was completely removed when inactivation of the interpositus was paired with electrical stimulation of the red nucleus. These findings speak to the important role of cerebellar structures in the extinction of discrete motor responses and provide important insight as to the validity of a particular theory of extinction.

Correlation of cerebellar volume with eyeblink conditioning in healthy subjects and in patients with cerebellar cortical degeneration

In the present study, acquisition and timing of conditioned eyeblink responses (CRs) were correlated with magnetic resonance imaging (MRI)-based cerebellar volume both in healthy human subjects and patients with cerebellar disease. Thirty-three healthy subjects and 25 patients with pure cortical cerebellar degeneration participated. Cerebellar volumes were measured for the cortex of the anterior lobe, the cortex of the posterior lobe, the white matter of the cerebellum and the cerebrum based on 3D MR images. CR parameters were assessed in a standard delay paradigm. In healthy subjects CR acquisition was significantly related to the volume of the grey matter of the posterior lobe, but neither to the volume of the grey matter of the anterior lobe, nor to the cerebellar white matter and nor to the cerebral volume. As expected, CR acquisition and volume of the cortex of the posterior lobe showed age-related decline in the controls. Furthermore, CR acquisition was significantly reduced in patients with cerebellar degeneration compared to controls. In the cerebellar group, however, no significant correlations between CR acquisition and any of the cerebellar volumes were observed. Floor effects are most likely responsible for this observation. Although CRs occurred significantly earlier in cerebellar patients compared to controls, no significant correlations between CR timing parameters and any of the cerebellar volumes were observed. Extending previous findings in healthy human subjects, age-related decline of the cerebellar cortex of the posterior lobe was related with a reduction of CR acquisition. Findings provide further evidence that the cerebellar cortex plays an important role in the acquisition of eyeblink conditioning in humans.

Hippocampal lesions in rats differentially affect long- and short-trace eyeblink conditioning

Extensive previous research has implicated the hippocampus as an important structure for the acquisition of trace eyeblink conditioning. Evidence from multiple species and various lesioning methods shows that the disruption of conditioned responding (CR) may be partially dependent on the relative lengths of the conditioned stimulus (CS) period and the trace interval. The present study systematically manipulated the length of the CS and the trace interval while matching the interstimulus intervals (ISI) in rats with or without ibotenic acid hippocampal lesions. The long-trace interval condition had a CS duration of 50 ms and a trace interval of 500 ms. The short-trace interval condition had a 500 ms CS and a 50 ms trace interval. We found that control animals in the long-trace interval condition learned at a slower rate than the control animals in the short-trace interval condition. Lesioned animals in both the trace conditions showed deficits in acquisition. Lesioned animals in the short-trace interval condition acquired conditioned responses at a rate almost identical to that of the control animals in the long-trace interval condition. CR onset latencies were impaired for lesioned animals. Peak latencies were not different, indicating no difference in the adaptiveness of the CRs. These results suggest that while the hippocampus is important for acquisition of trace eyeblink conditioning, performance also depends on the parameters used for the task. In particular, the relative lengths of the CS period and the trace interval appear to be important.

Ethanol-exposed neonatal rats are impaired as adults in classical eyeblink conditioning at multiple unconditioned stimulus intensities

Binge-like exposure to ethanol early in development results in neurotoxic impairments throughout the brain, including the cerebellum and brainstem. Rats exposed to ethanol, during a period of time commensurate with the human third trimester, also show deficits in classical eyeblink conditioning (EBC), a cerebellar-dependent associative learning procedure. The relationship between ethanol-mediated EBC deficits and the intensity of the unconditioned stimulus (US) was explored in the current study. Neonatal rats were intubated and infused with ethanol (EtOH rats), sham-intubated and given no ethanol (SI rats), or reared as unhandled controls (UC rats). As adults, all rats underwent 10 days of 350 ms delay eyeblink conditioning with a tone conditioned stimulus (CS) and one of three co-terminating periorbital shock US. The frequency and topography of the conditioned eyeblink response (CR) were impaired in EtOH rats relative to UC rats. EtOH rats produced fewer CRs, with longer onset latencies, at all US intensities. In contrast, CR amplitude was impaired in EtOH rats at the highest US intensity only. Following conditioning, the unconditioned eyeblink response (UR) was analyzed in subsets of rats from each treatment group at five US intensities. Early ethanol exposure did not impair UR peak amplitude. The deficits in CR production are proposed to result from ethanol-mediated damage within specific regions of the EBC neural circuit.

The involvement of the human cerebellum in eyeblink conditioning

Besides its known importance for motor coordination, the cerebellum plays a major role in associative learning. The form of cerebellum-dependent associative learning, which has been examined in greatest detail, is classical conditioning of eyeblink responses. The much advanced knowledge of anatomical correlates, as well as cellular and molecular mechanisms involved in eyeblink conditioning in animal models are of particular importance because there is general acceptance that findings in humans parallel the animal data. The aim of the present review is to give an update of findings in humans. Emphasis is put on human lesion studies, which take advantage of the advances of high-resolution structural magnetic resonance imaging (MRI). In addition, findings of functional brain imaging in healthy human subjects are reviewed. The former helped to localize areas involved in eyeblink conditioning within the cerebellum, the latter was in particular helpful in delineating extracerebellar neural substrates, which may contribute to eyeblink conditioning. Human lesion studies support the importance of cortical areas of the ipsilateral superior cerebellum both in the acquisition and timing of conditioned eyeblink responses (CR). Furthermore, the ipsilateral cerebellar cortex seems to be also important in extinction of CRs. Cortical areas, which are important for CR acquisition, overlap with areas related to the control of the unconditioned eyeblink response. Likewise, cortical lesions are followed by increased amplitudes of unconditioned eyeblinks. These findings are in good accordance with the animal literature. Knowledge about contributions of the cerebellar nuclei in humans, however, is sparse. Due to methodological limitations both of human lesion and functional MRI studies, at present no clear conclusions can be drawn on the relative contributions of the cerebellar cortex and nuclei.

Neonatal maternal separation alters adult eyeblink conditioning and glucocorticoid receptor expression in the interpositus nucleus of the cerebellum

Neonatal maternal separation alters learning and memory. Glucocorticoids also modulate adult learning and memory, and neonatal maternal separation alters forebrain glucocorticoid receptor (GR) concentrations. We used eyeblink classical conditioning to assess the effect of neonatal maternal separation on associative learning. We assessed delay eyeblink conditioning, GR expression, and total neuron number in the interpositus nucleus, a critical site of plasticity in eyeblink conditioning, in adult rats that had undergone either standard animal facilities rearing, handling for 15 min, or maternal separation for either 15 or 60 min per day on postnatal days 2-14. At 2-3 months of age, delay eyeblink classical conditioning was assessed. Brains were processed for GR immunohistochemistry, and GR expression in the interpositus nucleus was assessed using a computer-based densitometry system. Neuron counts and nuclear volumes were obtained from an alternate series of thionin-stained sections. Maternal separation significantly impaired eyeblink conditioning in male but not female rats. Handling and maternal separation did not significantly affect interpositus neuron number and volume. However, prolonged maternal separation significantly increased GR expression in the posterior interpositus in males, and increases were correlated with eyeblink conditioning. In female rats, maternal separation and handling did not significantly alter interpositus neuron number, volume, or GR protein expression, and GR expression did not correlate with eyeblink conditioning. Thus, neonatal maternal separation produces adult deficits in eyeblink conditioning and alterations in GR expression in its neural substrate in a sex-dependent manner.

Discrimination learning and reversal of the conditioned eyeblink reflex in a rodent model of autism

Offspring of rats exposed to valproic acid (VPA) on gestational day (GD) 12 have been advocated as a rodent model of autism because they show neuron loss in brainstem nuclei and the cerebellum resembling that seen in human autistic cases . Studies of autistic children have reported alterations in acquisition of classical eyeblink conditioning and in reversal of instrumental discrimination learning . Acquisition of discriminative eyeblink conditioning depends on known brainstem-cerebellar circuitry whereas reversal depends on interactions of this circuitry with the hippocampus and prefrontal cortex. In order to explore behavioral parallels of the VPA rodent model with human autism, the present study exposed pregnant Long-Evans rats to 600 mg/kg VPA on GD12 and tested their offspring from Postnatal Day (PND26-31) on discriminative eyeblink conditioning and reversal. VPA rats showed faster eyeblink conditioning, consistent with studies in autistic children . This suggests that previously reported parallels between human autism and the VPA rodent model with respect to injury to brainstem-cerebellar circuitry are accompanied by behavioral parallels when a conditioning task engaging this circuitry is used. VPA rats also showed impaired reversal learning, but this likely reflected "carry-over" of enhanced conditioning during acquisition rather than a reversal learning deficit like that seen in human autism. Further studies of eyeblink conditioning in human autism and in various animal models may help to identify the etiology of this developmental disorder.

From Malthus to motive: how the HPA axis engineers the phenotype, yoking needs to wants

The hypothalamo-pituitary-adrenal (HPA) axis is the critical mediator of the vertebrate stress response system, responding to environmental stressors by maintaining internal homeostasis and coupling the needs of the body to the wants of the mind. The HPA axis has numerous complex drivers and highly flexible operating characterisitics. Major drivers include two circadian drivers, two extra-hypothalamic networks controlling top-down (psychogenic) and bottom-up (systemic) threats, and two intra-hypothalamic networks coordinating behavioral, autonomic, and neuroendocrine outflows. These various networks jointly and flexibly control HPA axis output of periodic (oscillatory) functions and a range of adventitious systemic or psychological threats, including predictable daily cycles of energy flow, actual metabolic deficits over many time scales, predicted metabolic deficits, and the state-dependent management of post-prandial responses to feeding. Evidence is provided that reparation of metabolic derangement by either food or glucocorticoids results in a metabolic signal that inhibits HPA activity. In short, the HPA axis is intimately involved in managing and remodeling peripheral energy fluxes, which appear to provide an unidentified metabolic inhibitory feedback signal to the HPA axis via glucocorticoids. In a complementary and perhaps a less appreciated role, adrenocortical hormones also act on brain to provide not only feedback, but feedforward control over the HPA axis itself and its various drivers, as well as coordinating behavioral and autonomic outflows, and mounting central incentive and memorial networks that are adaptive in both appetitive and aversive motivational modes. By centrally remodeling the phenotype, the HPA axis provides ballistic and predictive control over motor outflows relevant to the type of stressor. Evidence is examined concerning the global hypothesis that the HPA axis comprehensively induces integrative phenotypic plasticity, thus remodeling the body and its governor, the brain, to yoke the needs of the body to the wants of the mind. Adverse side effects of this yoking under conditions of glucocorticoid excess are discussed.

Neuroscience and learning: lessons from studying the involvement of a region of cerebellar cortex in eyeblink classical conditioning

How the nervous system encodes learning and memory processes has interested researchers for 100 years. Over this span of time, a number of basic neuroscience methods has been developed to explore the relationship between learning and the brain, including brain lesion, stimulation, pharmacology, anatomy, imaging, and recording techniques. In this paper, we summarize how different research approaches can be employed to generate converging data that speak to how structures and systems in the brain are involved in simple associative learning. To accomplish this, we review data regarding the involvement of a particular region of cerebellar cortex (Larsell's lobule HVI) in the widely used paradigm of classical eyeblink conditioning. We also present new data on the role of lobule HVI in eyeblink conditioning generated by combining temporary brain inactivation and single-cell recording methods, an approach that looks promising for further advancing our understanding of relationships between brain and behavior.

Purkinje cell loss by OX7-saporin impairs acquisition and extinction of eyeblink conditioning

The current study examined the effects of globally depleting Purkinje cells in the cerebellar cortex with the immunotoxin OX7-saporin on acquisition and extinction of delay eyeblink conditioning in rats. Rats were given OX7-saporin or saline 2 wk before the start of eyeblink conditioning. The rats that reached a performance criterion of two consecutive days with 80% or greater conditioned responses were given 5 d of extinction training followed by 2 d of reacquisition training. Rats that received infusions of OX7-saporin had 77.2%-97.9% Purkinje cell loss and exhibited impaired acquisition and extinction. The amount of Purkinje cell loss was correlated with the magnitude of the acquisition and extinction impairments. The highest correlations between Purkinje cell number and the rate of acquisition were in lobule HVI and the anterior lobe. The highest negative correlation between Purkinje cell number and the percentage of conditioned responses during extinction was in the anterior lobe. The results indicate that cerebellar Purkinje cells, particularly in the anterior lobe and lobule HVI, play significant roles in acquisition and extinction of eyeblink conditioning.

Amygdalar unit activity during three learning tasks: eyeblink classical conditioning, Pavlovian fear conditioning, and signaled avoidance conditioning

Neural activity in central and basolateral amygdala nuclei (CeA and BLA, respectively) was recorded during delay eyeblink conditioning, Pavlovian fear conditioning, and signaled barpress avoidance. During paired training, the CeA exhibited robust learning-related excitatory activity during all 3 tasks. By contrast, the BLA exhibited minimal activity during eyeblink conditioning, while demonstrating pronounced increases in learning-related excitatory responsiveness during fear conditioning and barpress avoidance. In addition, the relative amount of amygdalar activation observed appeared to be related to the relative intensity of the unconditioned stimulus and somatic requirements of the task. Results suggest the CeA mediates the Pavlovian association between sensory stimuli and the BLA mediates the modulation of instrumental responding through the assignment of motivational value to the unconditioned stimulus.

Inactivation of sodium channel Scn8A (Nav1.6) in purkinje neurons impairs learning in Morris Water Maze and delay but not trace eyeblink classical conditioning

To examine the isolated effects of altered currents in cerebellar Purkinje neurons, the authors used Scn8a-super(flox/flox), Purkinje cell protein-CRE (Pcp-CRE) mice in which Exon 1 of Scn8a is deleted only in Purkinje neurons. Twenty male Purkinje Scn8a knockout (PKJ Scn8a KO) mice and 20 male littermates were tested on the Morris water maze (MWM). Subsequently, half were tested in 500-ms delay and half were tested in 500-ms trace eyeblink conditioning. PKJ Scn8a KO mice were impaired in delay conditioning and MWM but not in trace conditioning. These results provide additional support for the necessary participation of cerebellar cortex in normal acquisition of delay eyeblink conditioning and MWM and raise questions about the role, if any, of cerebellar cortex in trace eyeblink conditioning.

Trace eyeblink conditioning in human subjects with cerebellar lesions

Trace eyeblink conditioning was investigated in 31 patients with focal cerebellar lesions and 19 age-matched controls. Twelve patients presented with lesions including the territory of the superior cerebellar artery (SCA). In 19 patients lesions were restricted to the territory of the posterior inferior cerebellar artery (PICA). A 3D magnetic resonance imaging was used to determine the extent of the cortical lesion and possible involvement of cerebellar nuclei. Eyeblink conditioning was performed using a 40 ms tone as conditioned stimulus (CS) followed by a stimulus free trace-interval of 400 ms and a 100 ms air-puff as unconditioned stimulus (US). In SCA patients with lesions including parts of the cerebellar interposed nucleus trace eyeblink conditioning was significantly impaired. Pure cortical lesions of the superior cerebellum were not sufficient to reduce acquisition of trace conditioned eyeblink responses. PICA patients were not impaired in trace eyeblink conditioning. Consistent with animal studies the findings of the present human lesion study suggest that, in addition to forebrain areas, the interposed nucleus is of importance in trace eyeblink conditioning. Although cortical cerebellar areas appear less important in trace compared with delay eyeblink conditioning, the present data strengthen the view that cerebellar structures contribute to different forms of eyeblink conditioning paradigms.

Physiological and morphological development of the rat cerebellar Purkinje cell

Cerebellar Purkinje cells integrate multimodal afferent inputs and, as the only projection neurones of the cerebellar cortex, are key to the coordination of a variety of motor- and learning-related behaviours. In the neonatal rat the cerebellum is undeveloped, but over the first few postnatal weeks both the structure of the cerebellum and cerebellar-dependent behaviours mature rapidly. Maturation of Purkinje cell physiology is expected to contribute significantly to the development of cerebellar output. However, the ontogeny of the electrophysiological properties of the Purkinje cell and its relationship to maturation of cell morphology is incompletely understood. To address this problem we performed a detailed in vitro electrophysiological analysis of the spontaneous and intracellularly evoked intrinsic properties of Purkinje cells obtained from postnatal rats (P0 to P90) using whole-cell patch clamp recordings. Cells were filled with neurobiotin to enable subsequent morphological comparisons. Three stages of physiological and structural development were identified. During the early postnatal period (P0 to approximately P9) Purkinje cells were characterized by an immature pattern of Na(+)-spike discharge, and possessed only short multipolar dendrites. This was followed by a period of rapid maturation (from approximately P12 to approximately P18), consisting of changes in Na(+)-spike discharge, emergence of repetitive bursts of Na(+) spikes terminated by Ca(2+) spikes (Ca(2+)-Na(+) bursts), generation of the trimodal pattern, and a significant expansion of the dendritic tree. During the final stage (> P18 to P90) there were minor refinements of cell output and a plateau in dendritic area. Our results reveal a rapid transition of the Purkinje cell from morphological and physiological immaturity to adult characteristics over a short developmental window, with a close correspondence between changes in cell output and dendritic growth. The development of Purkinje cell intrinsic electrophysiological properties further matches the time course of other measures of cerebellar structural and functional maturation.

Vitamin E does not protect against neonatal ethanol-induced cerebellar damage or deficits in eyeblink classical conditioning in rats

BACKGROUND

Rodent studies have shown that heavy binge-like ethanol (EtOH) exposure during the brain growth spurt [postnatal days (PD) 4-9] causes cerebellar neuronal loss and deficits in cerebellar-mediated eyeblink classical conditioning (ECC). Oxidative stress has been implicated in EtOH-mediated brain damage, and studies using vitamin E have reported amelioration of EtOH-induced tissue damage, including protection in rats against EtOH-induced cerebellar Purkinje cell (PC) loss on PD 4 to 5. The purpose of this study was to determine whether dietary supplementation with vitamin E concurrent with binge EtOH exposure on PD 4 to 9 in rats would attenuate the cerebellar cell death and ECC deficits.

METHODS

Rat pups were given one of five different neonatal treatments: (1) intubation with EtOH in milk formula (twice daily, total dose 5.25 g/kg/day), (2) intubation with EtOH in milk formula supplemented with vitamin E (12.26 mg/kg/feeding), (3) intubation with milk formula that contained vitamin E only, (4) sham intubations, or (5) normally reared unintubated controls. Between PD 26 and 33, subjects received short-delay ECC for 3 consecutive days. Unbiased stereological cell counts were performed on cerebellar PCs of left cerebellar lobules I to VI and neurons of the interpositus nucleus. In a separate study with PD 4 pups, the effects of vitamin E on EtOH-induced expression of caspase-3 active subunits were assessed using Western blot analysis.

RESULTS

EtOH-treated groups showed significant deficits in acquisition of conditioned eyeblink responses and reductions in cerebellar PCs and interpositus nucleus neurons compared with controls. Vitamin E supplementation failed to protect against these deficits. Vitamin E also failed to protect against increases in caspase-3 active subunit expression induced by acute binge EtOH exposure on PD 4.

CONCLUSIONS

In contrast to the previously reported neuroprotective potential of antioxidants on EtOH-mediated cerebellar damage, vitamin E supplementation did not diminish EtOH-induced structural and functional damage to the cerebellum in this model of binge EtOH exposure during the brain growth spurt in rats.

A stress-induced anxious state in male rats: corticotropin-releasing hormone induces persistent changes in associative learning and startle reactivity

BACKGROUND

Exposure to intense inescapable stressors induces a persistent anxious state in rats. The anxious state is evident as increased sensory reactivity and enhanced associative learning.

METHODS

We examine whether similar neurobehavioral changes are observed after intracerebroventricular (ICV) administration of corticotropin releasing hormone (CRH). Two behaviors were observed: acoustic startle responses (ASRs) and acquisition of the classically conditioned eyeblink response. Male Sprague-Dawley rats were administered ICV CRH either in a single dose (1.0 microg/rat) or in three doses each separated by 30 min.

RESULTS

Exaggerated ASRs were evident 2 hours after either CRH treatment; however, only the rats given three injections exhibited a persistently exaggerated ASR apparent 24 hours after CRH treatment. Rats administered three injections of CRH also exhibited faster acquisition of the eyeblink conditioned response beginning 24 hours after treatment. Yet, we did not find evidence for a persistent activation of the HPA-axis response; three CRH injections did not lead to elevated basal plasma corticosterone levels the following morning.

CONCLUSIONS

Repeated treatment with CRH over a 1.5-hour period models some of the behavioral changes observed after exposure to intense inescapable stressors.

Acquisition, consolidation, reconsolidation, and extinction of eyelid conditioning responses require de novo protein synthesis

Memory, as measured by changes in an animal's behavior some time after learning, is a reflection of many processes. Here, using a trace paradigm, in mice we show that de novo protein synthesis is required for acquisition, consolidation, reconsolidation, and extinction of classically conditioned eyelid responses. Two critical periods of protein synthesis have been found: the first, during training, the blocking of which impaired acquisition; and the second, lasting the first 4 h after training, the blocking of which impaired consolidation. The process of reconsolidation was sensitive to protein synthesis inhibition if anisomycin was injected before or just after the reactivation session. Furthermore, extinction was also dependent on protein synthesis, following the same temporal course as that followed during acquisition and consolidation. This last fact reinforces the idea that extinction is an active learning process rather than a passive event of forgetting. Together, these findings demonstrate that all of the different stages of memory formation involved in the classical conditioning of eyelid responses are dependent on protein synthesis.

Differential mastication kinematics of the rabbit in response to food and water: implications for conditioned movement

Analysis of naturalistic chewing patterns may provide insight into mapping the neural substrates of jaw movement control systems, including their adaptive modification during the classically conditioned jaw movement (CJM) paradigm. Here, New Zealand White rabbits were administered food and water stimuli orally to evaluate the influence of stimulus consistency on masticatory pattern. Chewing patterns were recorded via video camera and movements were analyzed by computerized image analysis. The mandibular kinematics, specifically the extent of dorsal/ventral, medial/lateral, and rostral/caudal movement, were significantly larger in food-evoked than water-evoked chewing. Water-evoked chewing frequency, however, was significantly higher than that of food-evoked movements. In light of known cortical mastication modulatory centers, our findings implicate different neural substrates for the responses to food and water stimuli in the rabbit. A detailed delineation of jaw movement patterns and circuitry is essential to characterize the neural substrates of CJM.

Brain mechanisms of extinction of the classically conditioned eyeblink response

It is well established that the cerebellum and its associated circuitry are essential for classical conditioning of the eyeblink response and other discrete motor responses (e.g., limb flexion, head turn, etc.) learned with an aversive unconditioned stimulus (US). However, brain mechanisms underlying extinction of these responses are still relatively unclear. Behavioral studies have demonstrated extinction as an active learning process distinct from acquisition. Experimental data in eyeblink conditioning suggest that plastic changes specific to extinction may play an important role in this process. Both cerebellar and hippocampal systems may be involved in extinction of these memories. The nature of this phenomenon and identification of the neural substrates necessary for extinction of originally learned responses is the topic of this review.

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.

Impaired Cerebellar Learning in Children with Prenatal Alcohol Exposure: A Comparative Study of Eyeblink Conditioning in Children with ADHD and Dyslexia

Neuroanatomical and behavioral evidence indicate that the cerebellum is particularly vulnerable to the toxic effects of prenatal alcohol exposure. Recent research has shown impairments in eyeblink conditioning in rats following binge-like neonatal ethanol exposure. The neural substrates of eyeblink conditioning have been localized to the cerebellum and related brainstem mechanisms. The present study considered whether heavy prenatal alcohol exposure would result in similar impairments in eyeblink conditioning in children. A related purpose was to determine if eyeblink conditioning could discriminate between children with prenatal alcohol exposure and children diagnosed with attention deficit hyperactive disorder or developmental dyslexia. Fifty-three age-matched children [10 prenatal alcohol exposure (FAE), 16 attention deficit hyperactive disordered (ADHD), 14 children with dyslexia (DYS), 13 normal controls] were assessed on eyeblink conditioning in the delay paradigm. Children in the FAE and DYS groups failed to learn the conditioned response, producing longer latencies and poorly timed responses to the conditioning stimulus. Children with ADHD were impaired on measures of adaptively timed responses, although conditioned responses matched normal controls. The results suggest that children prenatally exposed to alcohol have deficits in cerebellar processing similar to those with dyslexia, and that these functional deficits are related to disabilities in learning.

Eyeblink Classical Conditioning to Auditory and Olfactory Stimuli: Performance Among Older Adults With and Without the Apolipoprotein E ε4 Allele

Patients with Alzheimer's disease (AD) demonstrate slowed acquisition of the conditioned response (CR) in eyeblink classical conditioning paradigms (EBCC), although it is unknown how early in the course of the disease CR acquisition is affected. This study investigated whether changes in the rate of CR acquisition were apparent in nondemented older adults at greater genetic risk for developing AD (i.e., carriers of the apolipoprotein E [APOE] epsilon 4 allele). Both epsilon 4+ and epsilon 4- participants demonstrated CR acquisition to auditory and olfactory CSs; however, rate of acquisition to the olfactory CS was significantly slower in epsilon 4+ persons. Both groups acquired the CR to an auditory CS at the same rate. Results support olfactory compromise in the earliest stages of the AD disease process. ((c) 2005 APA, all rights reserved).

Hallucinogens

Hallucinogens (psychedelics) are psychoactive substances that powerfully alter perception, mood, and a host of cognitive processes. They are considered physiologically safe and do not produce dependence or addiction. Their origin predates written history, and they were employed by early cultures in a variety of sociocultural and ritual contexts. In the 1950s, after the virtually contemporaneous discovery of both serotonin (5-HT) and lysergic acid diethylamide (LSD-25), early brain research focused intensely on the possibility that LSD or other hallucinogens had a serotonergic basis of action and reinforced the idea that 5-HT was an important neurotransmitter in brain. These ideas were eventually proven, and today it is believed that hallucinogens stimulate 5-HT(2A) receptors, especially those expressed on neocortical pyramidal cells. Activation of 5-HT(2A) receptors also leads to increased cortical glutamate levels presumably by a presynaptic receptor-mediated release from thalamic afferents. These findings have led to comparisons of the effects of classical hallucinogens with certain aspects of acute psychosis and to a focus on thalamocortical interactions as key to understanding both the action of these substances and the neuroanatomical sites involved in altered states of consciousness (ASC). In vivo brain imaging in humans using [(18)F]fluorodeoxyglucose has shown that hallucinogens increase prefrontal cortical metabolism, and correlations have been developed between activity in specific brain areas and psychological elements of the ASC produced by hallucinogens. The 5-HT(2A) receptor clearly plays an essential role in cognitive processing, including working memory, and ligands for this receptor may be extremely useful tools for future cognitive neuroscience research. In addition, it appears entirely possible that utility may still emerge for the use of hallucinogens in treating alcoholism, substance abuse, and certain psychiatric disorders.

Neurobiology of perceptual and motor timing in children with spina bifida in relation to cerebellar volume

The cerebellum is important for perceptual and motor timing in the mature brain, but the timing function of the cerebellum in the immature brain is less well understood. We investigated timing in children with spina bifida meningomyelocele (SB), a neural tube defect that involves cerebellar dysgenesis, and in age-matched controls. Specifically, we studied perceptual timing (judgements of 400 ms duration) and motor timing (isochronous motor tapping); measured cerebellar volumes; and related perceptual and motor timing to each other and to cerebellar volume measurements. Children with SB had impairments in the perception of duration (around 400 ms) but not frequency (around 3000 Hz), showing that their perceptual timing deficit was not a generalized auditory impairment. Children with SB had motor timing deficits on unpaced but not paced isochronous tapping, and their unpaced timing performance was associated with clock variance rather than with motor implementation. Perceptual and motor timing were correlated, suggesting that children with SB have impairments in a central timing mechanism. Children with SB, especially those with upper spinal cord lesions, had significant cerebellar volume reductions in grey and white matter, as well as different regional patterns of grey matter, white matter and CSF. Duration perception was correlated with cerebellar volumes, and the number of valid tapping trials was correlated with cerebellar volumes in the SB group, which data demonstrate structure-function relations between timing and cerebellar volumes.

Role of the cerebellum in eyeblink conditioning

The mammalian cerebellum is thought to participate in motor control and motor learning. The specific cerebellar contribution to these processes is not clear, however. Advances in understanding cerebellar function have been relatively slow, because, at least in most cases, the cerebellum appears to play only an ancillary role in the behaviors studied to date. A remarkable exception is classical conditioning of eyeblink responses in the rabbit. In this model, an intact cerebellum is critical for both the acquisition and expression of conditioned responses. Recent experiments suggest that the cerebellar role in classical conditioning might be similar in all mammals, including the human. Moreover, anticipatory defensive reflexes in other effector systems show a similar dependence on the intermediate cerebellum. Further developments in our understanding of cerebellar function will depend on examination of a wider array of cerebellar-involved neural networks. There is also need for the development of new experimental approaches to associative learning in both the nonhuman primate and the human.

Temporal Encoding in Fear Conditioning Revealed Through Associative Reflex Facilitation

Temporal encoding in Pavlovian fear conditioning was examined through conditional facilitation of the short-latency (Rl) component of the rat eyeblink reflex. Rats were fear-conditioned to a tone conditional stimulus (CS) with either a 3- or 9-s interstimulus interval (ISI) between CS onset and the onset of the grid-shock unconditional stimulus (US). Rl facilitation was tested over 2 days, in counterbalanced order, at a latency of 3 s and 9 s from CS onset. CS-produced Rl facilitation, the conditional response (CR), was 3-4 times larger when the test latency equaled the conditioning ISI. These results, coupled with the known neurophysiology of Rl facilitation, suggest that this CR could disclose differences in the time course of CS-generated output from the amygdala when driven by cortical versus subcortical CS-CR pathways.

Entorhinal inputs to dentate gyrus are activated mainly by conditioned events with long time intervals

Brain mechanisms of mammalian learning and memory have long been associated with the hippocampus. Although the role of the hippocampus in spatial behavior is well established, there is no general consensus on the function of the hippocampus in nonspatial tasks. Task-related changes in evoked potentials were first reported by Deadwyler and colleagues in the dentate gyrus, with a peak at 100 ms in rats trained in an auditory discrimination task (Deadwyler et al., Brain Res 161:211-225, 1979). Surprisingly, these results have not been confirmed by other investigators. In the present report, we set out to assess the task parameters that induce, modulate, and suppress this potential. Using multielectrode probes and current source density analysis, we monitored the entorhinal input to the dentate gyrus in behaving rats. Both differential and simple auditory conditioning led to the appearance of a large negative potential at 100 ms in the perforant path zone of the dentate gyrus. This negativity was found in averaged and in single-trial, evoked potentials. Current source density analysis revealed sinks in the perforant path zone of the molecular layer of the dentate gyrus with corresponding sources in the hilus. Once trained for differential conditioning, decrements of target probability consistently increased the amplitude of this negativity. When using a single-tone, stimulus-response task, the negative potential occurred with long (70-s), but not with short (10-s) intertrial intervals. Appearance of the potential coincided with a switch in response strategy and disappeared under stereotypical behavior. These data are best explained under the assumption that long intertrial intervals lead to transitions in task-related reference frames enabling a switch to more appropriate response strategies. Such transitions are not required during short interval stereotyped performance.

Inhibiting the expression of a classically conditioned behavior prevents its extinction

The underlying neuronal substrates and behavioral properties that might mediate extinction of the classically conditioned eye-blink response (CR) were examined. Four groups of rabbits were trained to perform the CR. Two of the groups then received either three or six sessions of tone-alone extinction training while the motor nuclei that mediate expression of the CR (facial nucleus and accessory abducens) were reversibly inactivated with microinjections of the GABA agonist muscimol. After these inactivation extinction sessions, rabbits received four more extinction sessions without inactivation. Two groups of controls received either three or six extinction sessions while saline vehicle was infused into the motor nuclei, followed by four sessions with no infusions. Saline infusions had no effect on extinction, and controls extinguished the CR normally over the first three to four sessions. In contrast, muscimol inactivation of the motor nuclei completely prevented any performance of CRs during the three or six inactivation extinction sessions. At the start of the four extinction sessions without inactivation, rabbits performed CRs at the same rate and amplitude as controls on their first extinction sessions. The muscimol rabbits then extinguished the CR normally over the four sessions without inactivation. In short, inactivation of the motor nuclei completely prevented any extinction of the eye-blink CR with no effect on subsequent extinction without inactivation. These results are discussed in terms of possible neuroanatomical loci that might mediate the extinction process as well as how effects of manipulating CR performance during extinction may affect the extinction process.

Role of the serotonin 5-HT(2A) receptor in learning

This study reviews the role of the serotonin 5-HT2A receptor in learning as measured by the acquisition of the rabbit's classically conditioning nictitating membrane response, a component of the eyeblink response. Agonists at the 5-HT2A receptor including LSD (d-lysergic acid diethylamide) enhanced associative learning at doses that produce cognitive effects in humans. Some antagonists such as BOL (d-bromolysergic acid diethylamide), LY53,857, and ketanserin acted as neutral antagonists in that they had no effect on learning, whereas others (MDL11,939, ritanserin, and mianserin) acted as inverse agonists in that they retarded learning through an action at the 5-HT2A receptor. These results were placed in the context of what is known concerning the anatomical distribution and electrophysiological effects of 5-HT2A receptor activation in frontal cortex and hippocampus, as well as the role of cortical 5-HT2A receptors in schizophrenia. It was concluded that the 5-HT2A receptor demonstrates constitutive activity, and that variations in this activity can produce profound alterations in cognitive states.

Stimulus generalization of conditioned eyelid responses produced without cerebellar cortex: implications for plasticity in the cerebellar nuclei

In Pavlovian eyelid conditioning and adaptation of the vestibulo-ocular reflex, cerebellar cortex lesions fail to completely abolish previously acquired learning, indicating an additional site of plasticity in the deep cerebellar or vestibular nucleus. Three forms of plasticity are known to occur in the deep cerebellar nuclei: formation of new synapses, plasticity at existing synapses, and changes in intrinsic excitability. Only a cell-wide increase in excitability predicts that learning should generalize broadly from a training stimulus to other stimuli capable of supporting learning, whereas the alternatives predict that learning should be relatively specific to the training stimulus. Here we show that deep nucleus plasticity, as assessed by conditioned eyelid responses produced without input from the cerebellar cortex, is relatively specific to the training conditioned stimulus (CS). We trained rabbits to a tone or light CS with periorbital stimulation as the unconditioned stimulus (US), and pharmacologically disconnected the cerebellar cortex during a posttraining generalization test. The short-latency conditioned responses unmasked by this treatment showed strong decrement along the dimension of auditory frequency and did not generalize across stimulus modalities. These results cannot be explained solely by a cell-wide increase in the excitability of deep nucleus neurons, and imply that an input-specific mechanism in the deep cerebellar nucleus operates as well.

Neural Substrates of Eyeblink Conditioning: Acquisition and Retention

Classical conditioning of the eyeblink reflex to a neutral stimulus that predicts an aversive stimulus is a basic form of associative learning. Acquisition and retention of this learned response require the cerebellum and associated sensory and motor pathways and engage several other brain regions including the hippocampus, neocortex, neostriatum, septum, and amygdala. The cerebellum and its associated circuitry form the essential neural system for delay eyeblink conditioning. Trace eyeblink conditioning, a learning paradigm in which the conditioned and unconditioned stimuli are noncontiguous, requires both the cerebellum and the hippocampus and exhibits striking parallels to declarative memory formation in humans. Identification of the neural structures critical to the development and maintenance of the conditioned eyeblink response is an essential precursor to the investigation of the mechanisms responsible for the formation of these associative memories. In this review, we describe the evidence used to identify the neural substrates of classical eyeblink conditioning and potential mechanisms of memory formation in critical regions of the hippocampus and cerebellum. Addressing a central goal of behavioral neuroscience, exploitation of this simple yet robust model of learning and memory has yielded one of the most comprehensive descriptions to date of the physical basis of a learned behavior in mammals.

GABA neurotransmission in the cerebellar interposed nuclei: involvement in classically conditioned eyeblinks and neuronal activity

The cerebellar interposed nuclei (IN) are an essential part of circuits that control classically conditioned eyeblinks in the rabbit. The function of the IN is under the control of GABAergic projections from Purkinje cells of the cerebellar cortex. The exact involvement of cerebellar cortical input into the IN during eyeblink expression is not clear. While it is known that the application of gamma-aminobutyric acid-A (GABA(A)) agonists and antagonists affects the performance of classically conditioned eyeblinks, the effects of these drugs on IN neurons in vivo are not known. The purpose of the present study was to measure the effects of muscimol and picrotoxin on the expression of conditioned eyeblinks and the activity of IN cells simultaneously. Injections of muscimol abolished conditioned responses and either silenced or diminished the activity of IN cells. Two injections were administered in each picrotoxin experiment. The first injection of picrotoxin slightly modified the timing and amplitude of the eyeblink, produced mild tonic eyelid closure, increased tonic activity of IN cells, and reduced the amplitude of the neural responses. The second injection of picrotoxin abolished conditioned responses, further increased tonic eyelid closure, dramatically elevated the tonic activity of IN cells, and in most cases, abolished neuronal responses. These results demonstrate that both GABA(A)-mediated inactivation and tonic up-regulation of IN cells can interrupt the expression of conditioned eyeblinks and that this behavioral effect is accompanied by the suppression of the neuronal activity correlates of the conditioned stimulus and response.

Pretraining NMDA receptor blockade in the basolateral complex, but not the central nucleus, of the amygdala prevents savings of conditional fear

The acquisition of conditional freezing is abolished by N-methyl-D-aspartate (NMDA) receptor antagonism in the basolateral complex of the amygdala (BLA) during fear conditioning, suggesting that memory formation is prevented. The present study examined whether there is residual memory, or "savings," for fear conditioning in rats trained under amygdaloid NMDA receptor blockade. Rats infused with D,L-2-amino-5-phosphonovalerate (APV) into the BLA or central nucleus of the amygdala (CEA) during fear conditioning did not acquire either auditory or contextual fear conditioning. However, savings of conditional fear was exhibited by rats infused with APV into the CEA but not the BLA. These results suggest that both the BLA and CEA play a critical role in the acquisition of conditional fear but that the BLA is able to process and retain some aspects of aversive memories in the absence of the CEA.

Role of the anterior cingulate cortex in the control over behavior by Pavlovian conditioned stimuli in rats

To investigate the contribution of the anterior cingulate cortex (ACC) to stimulus-reward learning, rats with lesions of peri- and postgenual ACC were tested on a variety of Pavlovian conditioning tasks. Lesioned rats learned to approach a food alcove during a stimulus predicting food, and responded normally for conditioned reinforcement. They also exhibited normal conditioned freezing and Pavlovian-instrumental transfer, yet were impaired at autoshaping. To resolve this apparent discrepancy, a further task was developed in which approach to the food alcove was under the control of 2 stimuli, only 1 of which was followed by reward. Lesioned rats were impaired, approaching during both stimuli. It is suggested that the ACC is not critical for stimulus-reward learning per se, but is required to discriminate multiple stimuli on the basis of their association with reward.

Impaired conditional discrimination learning in social phobia

Eyelid conditional discrimination learning (ECDL) is a test of discriminative aversive conditioning. It places minimal demands on motivation and was shown to selectively test temporal lobe function. Twenty-five unmedicated social phobia (SP) patients (mean age 29.5 +/- 7.0 years), diagnosed according to DSM-IV criteria, and 25 age- and gender-matched healthy controls (HC, mean age 34.0 +/- 8.6 years) were examined with an ECDL paradigm. In the experiment two differently colored stimuli are randomly presented. Only one of the stimuli (reinforced trial) is followed by an aversive airpuff to the cornea, as opposed to unreinforced trials not followed by an airpuff. Conditioned responses (CRs) consist of reflex eyelid closures already upon light presentation. HC as well as SP patients showed a significant difference between reinforced and unreinforced trials. In SP patients, CR frequency did not increase during the ECDL task, while HCs showed appropriate conditional discrimination ability. Thus the results indicate an impairment of adequate behavior modification in an aversive conditioning task in SP.

Comparison of eyeblink conditioning in patients with superior and posterior inferior cerebellar lesions

The aim of the present study was to compare eyeblink conditioning in cerebellar patients with lesions including the territory of the superior cerebellar artery (SCA) and in patients with lesions restricted to the territory of the posterior inferior cerebellar artery (PICA). The cerebellar areas known to be most critical in eyeblink conditioning based on animal data (i.e. Larsell lobule H VI and interposed nucleus) are commonly supplied by the SCA. Eyeblink conditioning was expected to be impaired in SCA, but not in PICA patients. A total of 27 cerebellar patients and 25 age-matched controls were tested. Cerebellar lesions were primarily unilateral (n = 20). Most patients suffered from ischaemic infarctions of the SCA (n = 11) or the PICA (n = 13). The other patients presented with cerebellar tumours (n = 2) and cerebellar agenesis (n = 1). The extent of the cortical lesion (i.e. which lobuli were affected) and possible involvement of the cerebellar nuclei was determined by 3D-MRI. As expected, the ability to acquire classically conditioned eyeblink responses was significantly reduced in the group of all cerebellar patients compared with the controls. In the patients with unilateral cerebellar lesions, conditioning deficits were present ipsilaterally. In SCA patients with lesions including hemispheral lobules VI and Crus I, eyeblink conditioning was significantly reduced on the affected side compared with the unaffected side. No significant difference between the affected and unaffected sides was present in patients with lesions restricted to the common PICA territory (i.e. Crus II and below). Conditioning deficits were neither significantly different in SCA patients with pure cortical lesions compared with SCA patients with additional nuclear impairment nor in SCA patients with unilateral lesions compared with SCA patients with bilateral lesions. To summarize, unilateral cortical lesions of the superior cerebellum appear to be sufficient to reduce eyeblink conditioning in humans significantly.

The Ontogeny of Human Learning in Delay, Long-Delay, and Trace Eyeblink Conditioning

The ontogeny of associative learning in delay (750-ms conditional stimulus [CS], 650-ms interstimulus interval [ISI]), long-delay (1,350-ms CS, 1,250-ms ISI), and trace (750-ms CS, 500-ms trace interval, 1,250-ms ISI) eyeblink conditioning was examined in 5-month-old human infants and adults. Infants and adults showed different acquisition rates but reached equivalent asymptotes of conditional responses (CRs) in standard delay conditioning. In long-delay and trace conditions, infants exhibited less robust conditioning than adults and minimal ability to appropriately time CRs. During infancy, the ISI, rather than the conditioning procedure, predicted rate and effectiveness of CRs. These findings suggest that higher order cognitive abilities begin emerging early in development. Across ontogeny, however, there are changes in the limits and parameters that support associative learning.

A common role for psychotropic medications: memory impairment

The psychopathologic profile of mental disorders is very diverse and psychotropic medications used to treat them differ in their chemical structure. Nevertheless, these drugs share these four characteristics: delayed onset of clinical response, not one of them can be said to cure, there is a high number of non-responders, and the mechanism responsible for their therapeutic action is not known. It is hypothesized that the action of psychotropic medications is memory impairment, understanding memory as the trace left in the nervous system not only by individual experiences but also by genetic and epigenetic phenomena. It is suggested that it would be beneficial to translate some research strategies from the neurobiology of learning and memory to the study of the effects of psychotropic medications. The hypothesis is briefly assessed according to the following three criteria: (a). the comparison between the molecular effects of psychotropic medications and the so-called molecular biology of learning and memory, (b). the effects of these drugs, preferentially after chronic use, on memory tests, and (c). the effects of drugs that impair memory on tests used for screening psychotropic medications. Finally, some general suggestions for future research are pointed out.

mGluR1 in cerebellar Purkinje cells is required for normal association of temporally contiguous stimuli in classical conditioning

In metabotropic glutamate receptor-subtype 1 (mGluR1)-null (mGluR1-/-) mice, cerebellar long-term depression (LTD) and several forms of memory are impaired. However, because mGluR1 is expressed in various brain regions in wild-type mice, it has been difficult to identify which type of memory depends on mGluR1 expressed in a given brain region. Furthermore, severe ataxia in mGluR1-/- mice complicated interpretation of the data from non-cerebellum-dependent tasks. We have generated mGluR1-rescue mice, which express mGluR1 only in Purkinje cells (PCs) of their cerebellum, by introducing the mGluR1alpha transgene into mGluR1-/- mice under the control of a PC-specific promoter. The mGluR1-rescue mouse has normal LTD and displays no apparent ataxia. Therefore, this mouse is the first animal model in which effects of mGluR1 deficiency outside PCs can be studied without cerebellar dysfunction. We used three eyeblink conditioning paradigms with different temporal specificities between conditioned stimulus (CS) and unconditioned stimulus (US). Delay conditioning, in which CS and US coterminate, was impaired in mGluR1-/- mice but normal in mGluR1-rescue mice. However, both strains of mice displayed severe impairment in trace conditionings, in which a stimulus-free interval of 250 or 500 ms intervened between CS and US. We also examined social transmission of food-preference and novel-object-recognition memory tests. In these tasks, mGluR1-rescue mice showed normal short-term but impaired long-term memory. We conclude that mGluR1 in PCs is indispensable for normal learning of association of temporally contiguous stimuli in associative conditioning. In contrast, mGluR1 in other cell types is required for associating discontiguous stimuli and long-term memory formation in nonspatial hippocampus-dependent learning.