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.     

New Directions for a Classical Paradigm: Human Eyeblink Conditioning

Abstract—The knowledge base on neural substrates an mechanisms involved in classical eyeblink conditioning makes it an ideal paradigm for investigating fundamental issues in learning and memory. New applications for the model system presented here include its use in (a) assessment to evaluate neurocognitive development in infancy, (b) theory building in abnormal psychology to test relationships between obsessive-compulsive behavior and learning rate, (c) evaluation of hypotheses about brain memory systems, and (d) exploration of the role of brain structures such as the cerebellum in learning and timing. Human eyeblink conditioning is a prototype of the utility of a model system that has become well characterized at both the behavioral and the neurobiological levels.     

Using Eyeblink Classical Conditioning as a Test of the Functional Consequences of Exposure of the Developing Cerebellum to Alcohol

Exposure of the developing brain to alcohol produces profound Purkinje cell loss in the cerebellum, and deficits in tests of motor coordination. However, the precise relationship between these two sets of findings has been difficult to determine. Eyeblink classical conditioning is known to engage a discrete brainstem-cerebellar circuit, making it an ideal test of cerebellar functional integrity after developmental alcohol exposure. In eyeblink conditioning, one of the deep cerebellar nuclei, the interpositus nucleus, as well as specific Purkinje cell populations, are sites of convergence for CS and US information. A series of studies have shown that eyeblink conditioning is impaired in both weanling and adult rats given binge-like exposure to alcohol as neonates, and that these deficits can be traced, at least in part, to impaired activation of cerebellar interpositus nucleus neurons and to an overall reduction in the deep cerebellar nuclear cell population. Because particular cerebellar cell populations are utilized in well-defined ways during eyeblink conditioning, conclusions regarding specific changes in the mediation of behavior by these cell populations are greatly strengthened. Further studies will be directed towards the impact of early exposure to alcohol on the functionality of specific Purkinje cell populations, as well as towards brainstem areas that process the tone CS and the somatosensory US.     

Timing in Eyeblink Classical Conditioning and Timed-Interval Tapping

Abstract—The cerebellum is implicated in interval timing for diverse tasks including eyeblink classical conditioning (EBCC) and repetitive tapping. We examined performance on both tasks across identical intervals ranging from 325 to 550 ms. In five weekly sessions, 23 participants used a different interval each week, both as the target for tapping and as the delay interval in EBCC. Changes in variability as a function of the tapping or delay interval were assessed using regression analyses. The slope for repetitive tapping was comparable to two measures of temporal acuity in EBCC, onset and peak latency of the conditioned response. Each of 80 additional participants was assessed in one session at one of four tapping and delay intervals. Results were similar to those observed in the repeated measures group. These findings provide further evidence that EBCC and repetitive tapping utilize common mechanisms for representing temporal information.     

Human Eyeblink Classical Conditioning: Effects of Manipulating Awareness of the Stimulus Contingencies

Obsessive-compulsive disorder (OCD) is an intrusive and debilitating condition in which the individual experiences uncontrollable thoughts, compulsions, and urges. Successful treatments for OCD are based on Mowrer's theory of fear and avoidance behavior, which predicts that OCD subjects should show accelerated associative conditioning. This prediction was tested in two experiments that com-pared the classical eyeblink conditioning of OCD-like and control college students. OCD and control subjects learned normally and similarly when the conditioning procedure was accompanied by an active visual search background task (Experiment 1). However, when the background task was changed so that subjects passively viewed neutral pictures, OCD subjects conditioned significantly faster than control subjects (Experiment 2). Overall, the performance of all subjects in Experiment 1 was superior to the performance of subjects in Experiemnt 2.     

Effects of Emotional Valence and Arousal Manipulation on Eyeblink Classical Conditioning and Autonomic Measures

Using a classical eyeblink conditioning paradigm, we have previously shown that the rate of acquisition of a conditioned response may be manipulated by engaging subjects in background tasks of varying complexity concurrent to conditioning. To further examine the influence of the background environment on conditioning, a picture set designed to elicit emotional responses, the International Affective Picture System (IAPS), was presented to subjects during classical eyeblink conditioning. The results suggest that eyeblink conditioning does appear to be sensitive to contextual manipulations of arousal. Pictures rated as very arousing were found to engage subjects enough to enhance learning, although not to the point that autonomic functions were significantly altered between picture groups. We suggest that group differences in learning may be a result of either novelty of, or vigilance to, interesting pictures rather than as a direct result of physiological arousal.     

Classical Delay Eyeblink Conditioning in in 4- and 5-Month-Old Human Infants

Abstract-Simple delay classical eyeblink conditioning, using a tone conditioned stimulus (CS) and airpuff unconditioned stimulus (US), was studied in cross-sectional samples of 4- and 5-month-old healthy, full-term infants. Infants received two identical training sessions, 1 week apart. At both ages, infants experiencing paired tones and air-puffs demonstrated successful conditioning over two sessions, relative to control subjects who had unpaired training. Conditioning was not evident, however, during the first session. Two additional groups of 5-month-olds received varied experiences during Session 1, either unpaired presentations of the CS and US or no stimulus exposure, fol-lowed by paired conditioning during Session 2. Results from these groups suggest that the higher level of conditioning observed following two sessions of paired conditioning was not the result of familiarity with the testing environment or the stimuli involved but, rather, the result of retention of associative learning not expressed during the first conditioning session.     

The Effect of Scopolamine in Older Rabbits Tested in the 750 ms Delay Eyeblink Classical Conditioning Procedure

We investigated the effect of several doses of scopolamine in older rabbits that were trained for 20 days in the 750 ms delay eyeblink classical conditioning procedure. Our aim was to determine if the scopolamine-injected older rabbit would be a useful model for testing drugs for cognition enhancement in Alzheimer's disease (AD). A total of 39 rabbits with a mean age of 31 months received classical eyeblink conditioning with daily injections of 0.25, 0.75, or 1.5 mg/kg scopolamine hydrobromide or sterile saline vehicle. Doses of 0.75 and 1.5 mg/kg scopolamine significantly impaired acquisition, whereas acquisition was not significantly impaired with 0.25 mg/kg scopolamine. Results exhibit parallels in performance on delay eyeblink classical conditioning between scopolamine-treated older rabbits and human patients diagnosed with AD.     

Fear Develops to the Conditioned Stimulus and to the Context during Classical Eyeblink Conditioning in Rats

In classical eyeblink conditioning, non-specific emotional responses to the aversive shock unconditioned stimulus (US), which are presumed to coincide with the development of fear, occur early in conditioning and precede the emergence of eyeblink responses. This two-process learning model was examined by concurrently measuring fear and eyeblink conditioning in the freely moving rat. Freezing served as an index of fear in animals and was measured during the inter-trial intervals in the training context and during a tone conditioned stimulus (CS) presented in a novel context. Animals that received CS-US pairings exhibited elevated levels of fear to the context and CS early in training that decreased over sessions, while eyeblink conditioned responses (CRs) developed gradually during acquisition and decreased during extinction. Random CS-US presentations produced a similar pattern of fear responses to the context and CS as paired presentations despite low eyeblink CR percentages, indicating that fear responding was decreased independent of high levels of learned eyeblink responding. The results of paired training were consistent with two-process models of conditioning that postulate that early emotional responding facilitates subsequent motor learning, but measures from random control animals demonstrate that partial CS-US contingencies produce decrements in fear despite low levels of eyeblink CRs. These findings suggest a relationship between CS-US contingency and fear levels during eyeblink conditioning, and may serve to clarify further the role that fear conditioning plays in this simple paradigm.     

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.     

Localizing Localization: The Role of Working Memory in Auditory Localization

It is unclear from current accounts of working memory which, if any, of its components might be involved in our ability to specify the location of a sound source. A series of studies were performed to assess the degree of interference in localization of broadband noise, by a concurrent articulatory suppression (articulatory loop—Experiment 1), serial recall (phonological store and articulatory loop—Experiment 2), and Paced Visual Serial Addition Test (central executive—Experiment 3). No significant disruption of auditory localization was revealed by the first two experiments, ruling out a role for the phonological loop in auditory localization. In Experiment 3, a large degree of error was exhibited in localization, when performed concurrently with the addition task, indicating a requirement for central resources. This suggestion is confirmed by comparison of localization performance across all three studies, which demonstrates a clear deterioration in performance as the demand of concurrent tasks on central resources increases. Finally, concurrent localization was shown to disrupt the primacy portion of the serial position curve, as well as performance on the Paced Visual Serial Addition Test.     

From Incubation to Insight: Working Memory and the Role of the Cerebellum

An experiment involving 90 students in the 1st, 3rd, and 5th grades investigated how visual examples and grade (our surrogate for age) affected variability in a drawing task. The task involved using circles as the main element in a set of drawings. There were two examples: One was simple and single (a smiley face inside a circle); the other, complex and dual (a fishbowl extending outside a circle and a bicycle using two circles). There were significant effects of both example and grade on variability. Between-grades, 3rd and 5th graders were more variable than 1st graders with the complex (but not the simple) set of examples. Within-grades, 3rd and 5th graders were more variable with the complex (compared to the simple) set of examples. First graders' variability levels did not change with examples. The discussion focuses on how examples have and should be used to increase variability in drawings of both younger and older children.     

A Comparison of Latent Inhibition and Learned Irrelevance Pre-Exposure Effects in Rabbit and Human Eyeblink Conditioning

The learning of an association between a CS and a US can be retarded by unreinforced presentations of the CS alone (termed latent inhibition or LI) or by un-correlated presentations of the CS and US (termed learned irrelevance or LIRR). In rabbit eyeblink conditioning, there have been some recent failures to replicate LI. LIRR has been hypothesized as producing a stronger retardation effect than LI based on both empirical studies and computational models. In the work presented here, we examined the relative strength of LI and LIRR in eyeblink conditioning in rabbits and humans. In both species, a number of preexposure trials sufficient to produce LIRR failed to produce LI (Experiments 1 & 3). Doubling the number of CS pre-exposures did produce LI in rabbits (Experiment 2), but not in humans (Experiment 4). LI was demonstrated in humans only after manipulations including an increased inter-trial interval or ITI (Experiment 5). Overall, it appears that LIRR is a more easily producible pre-exposure retardation effect than LI for eyeblink conditioning in both rabbits and humans. Several theoretical mechanisms for LI including the conditioned attention theory, stimulus compression, novelty, and the switching theory are discussed as possible explanations for the differences between LIRR and LI. Overall, future work involving testing the neural substrates of pre-exposure effects may benefit from the use of LIRR rather than LI.     

Effects of Early Hippocampal Lesions on Trace, Delay, and Long-Delay Eyeblink Conditioning in Developing Rats

The effects of bilateral hippocampal aspiration lesions on later acquisition of eyeblink conditioning were examined in developing Long-Evans rat pups. Lesions on postnatal day (PND) 10 were followed by evaluation of trace eyeblink conditioning (Experiment 1) and delay eyeblink conditioning (Experiment 2) on PND 25. Pairings of a tone conditioned stimulus (CS) and periocular shock unconditioned stimulus (US, 100 ms) were presented in one of three conditioning paradigms: trace (380 ms CS, 500 ms trace interval, 880 ms interstimulus interval [ISI]), standard delay (380 ms CS, 280 ms ISI), or long delay (980 ms CS, 880 ms ISI). The results of two experiments indicated that hippocampal lesions impaired trace eyeblink conditioning more than either type of delay conditioning. In light of our previous work on the ontogeny of trace, delay, and long-delay eyeblink conditioning (Ivkovich, Paczkowski, & Stanton, 2000) showing that trace and long-delay eyeblink conditioning had similar ontogenetic profiles, the current data suggest that during ontogeny hippocampal maturation may be more important for the short-term memory component than for the long-ISI component of trace eyeblink conditioning. The late development of conditioning over long ISIs may depend on a separate process such as protracted development of cerebellar cortex.     

The Lateralized Linguistic Cerebellum: A Review and a New Hypothesis

During the past 2 decades the collaboration across disciplines and the methodologic and conceptual advances of contemporary neuroscience have brought about a substantial modification of the traditional view of the cerebellum as a mere coordinator of autonomic and somatic motor functions. Growing insights in the neuroanatomy of the cerebellum and its interconnections, evidence from functional neuroimaging and neurophysiological research, and advancements in clinical and experimental neuropsychology have established the view that the cerebellum participates in a much wider range of functions than conventionally accepted. This increase of insight has brought to the fore that the cerebellum modulates cognitive functioning of at least those parts of the brain to which it is reciprocally connected. This article reviews the recently acknowledged role of the cerebellum in cognition and addresses in more detail experimental and clinical data disclosing the modulatory role of the cerebellum in various non-motor language processes such as lexical retrieval, syntax, and language dynamics. In agreement with the findings indicating a topographical organization of the cerebellar structures involved in language pathology we advance the concept of a "lateralized linguistic cerebellum." In our view crossed cerebral diaschisis processes, reflecting a functional depression of supratentorial language areas due to reduced input via cerebellocortical pathways, might represent the relevant pathomechanism for linguistic deficits associated with cerebellar pathology.     

Dissociating Basal Forebrain and Medial Temporal Amnesic Syndromes: Insights from Classical Conditioning

In humans, anterograde amnesia can result from damage to the medial temporal (MT) lobes (including hippocampus), as well as to other brain areas such as basal forebrain. Results from animal classical conditioning studies suggest that there may be qualitative differences in the memory impairment following MT vs. basal forebrain damage. Specifically, delay eyeblink conditioning is spared after MT damage in animals and humans, but impaired in animals with basal forebrain damage. Recently, we have likewise shown delay eyeblink conditioning impairment in humans with amnesia following anterior communicating artery (ACoA) aneurysm rupture, which damages the basal forebrain. Another associative learning task, a computer-based concurrent visual discrimination, also appears to be spared in MT amnesia while ACoA amnesics are slower to learn the discriminations. Conversely, animal and computational models suggest that, even though MT amnesics may learn quickly, they may learn qualitatively differently from controls, and these differences may result in impaired transfer when familiar information is presented in novel combinations. Our initial data suggests such a two-phase learning and transfer task may provide a double dissociation between MT amnesics (spared initial learning but impaired transfer) and ACoA amnesics (slow initial learning but spared transfer). Together, these emerging data suggest that there are subtle but dissociable differences in the amnesic syndrome following damage to the MT lobes vs. basal forebrain, and that these differences may be most visible in non-declarative tasks such as eyeblink classical conditioning and simple associative learning.