Reacquisition of classical conditioning after removal of cerebellar cortex

Summary We trained rabbits with white noise and light conditioned stimuli and a face shock unconditioned stimulus for classical conditioning of the nictitating membrane response and then removed the ipsilateral cerebellar cortex by aspiration. Larsell's hemisphere lobule VI was completely removed in 5 rabbits; the pattern of degeneration in the inferior olive matches the projections to HVI reported in experiments with horseradish peroxidase. All rabbits showed an initial abolition of conditioned responses but then relearned within two days. This indicates that cerebellar cortical lobule HVI normally is involved but is not necessary for classical conditioning.     

Functional neuroanatomical correlates of electrodermal activity: A positron emission tomographic study

To reveal areas in the central nervous system of importance for electrodermal control, regional cerebral blood flow (rCBF) was correlated to nonspecific skin conductance fluctuations (NSF) during aversive and nonaversive conditions. Participants viewed a TV screen displaying white noise or snake videotapes presented both with and without electric shocks given to the right hand. H₂¹⁵O positron emission tomography was used to measure rCBF, and the constant voltage technique was used to measure NSF from the left hand. Electrodermal activity was positively related to rCBF in the left primary motor cortex (MI, Brodmann's Area 4) and bilaterally in the anterior (Areas 24 and 32) and posterior cingulate cortex (Area 23). Negative relations were observed bilaterally in the secondary visual cortex (Areas 18 and 19) and the right inferior parietal cortex (Area 39), with a tendency also for the right insular cortex (Areas 13, 15, and 16). Because results from lesion and stimulation studies in humans converge with the present imaging results, we conclude that the cingulum and the motor cortex, in addition to the parietal and possibly the insular cortex, form part of one or several distributed neural network(s) involved in electrodermal control. Because these areas also support anticipation, affect, and locomotion, electrodermal responses seem to reflect cognitively or emotionally mediated motor preparation.     

Cortical areas and the selection of movement: a study with positron emission tomography

Summary Regional cerebral blood flow was measured in normal subjects with positron emission tomography (PET) while they performed five different motor tasks. In all tasks they had to moved a joystick on hearing a tone. In the control task they always pushed it forwards (fixed condition), and in four other experimental tasks the subjects had to select between four possible directions of movement. These four tasks differed in the basis for movement selection. A comparison was made between the regional blood flow for the four tasks involving movement selection and the fixed condition in which no selection was required. When selection of a movement was made, significant increases in regional cerebral blood flow were found in the premotor cortex, supplementary motor cortex, and superior parietal association cortex. A comparison was also made between the blood flow maps generated when subjects performed tasks based on internal or external cues. In the tasks with internal cues the subjects could prepare their movement before the trigger stimulus, whereas in the tasks with external cues they could not. There was greater activation in the supplementary motor cortex for the tasks with internal cues. Finally a comparison was made between each of the selection conditions and the fixed condition; the greatest and most widespread changes in regional activity were generated by the task on which the subjects themselves made a random selection between the four movements.     

Individual Differences in Autonomic Response: Conditioned Association or Conditioned Fear?

Cluster analysis was used to define three groups of subjects whose conditioned heart rate response emphasized either acceleration, deceleration, or moderate deceleration. A subject pool (N = 148) was generated from four separate studies of differential classical conditioning in which colored slides served as conditioned stimuli (CSs) and the unconditioned stimulus (UCS) was aversive auditory noise. Both the statistically generated Accelerator and Decelerator groups responded with a significant late interval deceleration to CS+. However, only Accelerators also displayed a significant mid-interval heart rate increase to CS+. Conditioned electrodermal responses were significantly more resistant to extinction for Accelerators than for the other two cluster groups. Accelerators also differed from Decelerators in that their affective judgments of the slide stimuli became less positively valent and less dominant from pre- to post-conditioning, effects not found for Decelerators. Moderate Decelerators produced mixed results across the several psychophysiological and verbal measures of conditioning, resembling Accelerators in their verbal report change, and Decelerators in their rapid electrodermal extinction. It is suggested that cluster assignment may reflect subjects' pre-conditioning learning set. All successfully conditioned subjects appear to learn a relationship between stimuli such that the appearance of the CS+ prompts an anticipatory orienting response (late interval heart rate deceleration). Accelerators differ from the other two groups in that they also condition a defensive response which is associated with a change in emotional judgments of the stimuli and may represent covert preparation for avoidance. The relationships between defensive responding, avoidance, and the concept of fear are considered, and the problem of desynchrony in emotional change (i.e., the Moderate Decelerators) is addressed. Finally, parallels are drawn between results from classical conditioning and clinical studies of fear and phobia, and further suggestions are made for utilizing the conditioning paradigm in the study of emotion.     

Retention of Differential Autonomic Conditioning and Memory for Conditional Stimulus Relationships

Corollary to the hypothesis that awareness of the conditional stimulus relationships is necessary for the acquisition of differential conditioning, it was predicted that memory for the conditional stimulus relationships (i.e., awareness at retention testing) would be necessary for the retention of differential autonomic conditioning. Groups of 20 subjects each were tested for retention of differential skin conductance and vasomotor conditioning, differential expectancies of the unconditional stimulus, and memory for the CS-US relationships either 1 day or 28 days after initial acquisition. A continuous measure of expectancy of the unconditional stimulus was obtained during initial acquisition and retention testing. Retention testing consisted of a series of unreinforced presentations of the conditional stimuli and a reacquisition series. The 28-day interval resulted in more forgetting of the conditional stimulus relationships and greater retention loss of differential autonomic conditioning and differential US expectancies than did the 1-day interval. Within the group tested after 28 days, retention loss was related to the subjects' post-experimental reports of whether or not they remembered the CS-US relationships. Subjects reporting having forgotten showed complete retention loss of differential autonomic conditioning and differential US expectancies while subjects reporting having remembered showed good retention, similar to that shown after the 1-day retention interval. The hypothesis that memory for the conditional stimulus relationships is necessary for retention of autonomic conditioning was supported. It was also found that long-term memory for the conditional stimulus relationships was related to greater autonomic responsivity during initial acquisition.     

The Role of Awareness in Human Differential Autonomic Classical Conditioning: The Necessary-Gate Hypothesis

A “necessary-gate” hypothesis is proposed regarding the relationship between awareness of the CS-UCS relationship and autonomic classical conditioning. The hypothesis is that awareness is a necessary but not sufficient condition, and a gate but not analog condition, for human differential autonomic classical conditioning. Evidence in support of the hypothesis is reviewed and directions for future research and theory development are suggested.     

Right hemisphere representation of autonomic conditioning to facial emotional expressions

In this experiment, a lateralized right hemisphere effect was found for electrodermal associative learning to facial emotional expressions. Sixty-two subjects were presented simultaneously with a slide of a happy face in the right or left visual half field (VHF) and a slide of an angry face in the opposite VHF. Four groups were formed by the combination of the two VHF positions of angry/happy faces and the administration/omission of shock unconditioned stimuli. The results showed that simultaneous presentation of the angry face to the right hemisphere and the happy face to the left hemisphere, together with shock, resulted in a strong conditioned association with the angry face and a relatively weak association with the happy face. Furthermore, simultaneous presentation of the angry face to the left hemisphere and the happy face to the right hemisphere, together with shock, resulted in a relatively weak association with both stimuli. No significant differences were found for the no-shock control groups. The present results confirm previous findings of a right hemisphere advantage for representation of associative learning.     

Cortical activation during color discrimination task in macaques as revealed by positron emission tomography

Physiological and lesion studies have shown that the anterior inferior temporal (IT) cortex (aITC) is involved in the color vision of macaque monkeys. However, some functional imaging studies using awake monkeys contradicted the involvement of aITC in color vision. Thus, in most of the imaging studies, cortical activation has been observed during a fixation task. However, because the neuronal activity of aITC is highly affected by the behavioral task, it is desirable to investigate cortical activity during a color discrimination task to determine the functional role of aITC in the color vision of macaque monkeys. In this study, we investigated the cortical activity of aITC of macaque monkeys during color discrimination by positron emission tomography. Two monkeys were trained in a color discrimination task. Cortical areas involved in color processing were investigated by comparing activities during the color discrimination and lever release tasks. In addition to area V4 and the posterior IT cortex (pITC), we found color-related activities in the anterior IT gyrus. Consistent activation was observed in the region posterior to the anterior medial temporal sulcus (AMTS), although the exact location and the size of activations differed between monkeys and hemispheres. We also found color-related activities in the anterior portion of the superior temporal sulcus (STS), suggesting its involvement in the color vision. The present results revealed that aITC is involved in the color vision of macaque monkeys by a functional imaging technique.     

Cortical control of optokinetic nystagmus in humans: a positron emission tomography study

 Positron emission tomography (PET) was used to address the issue of physiological changes in the cerebral cortex associated to optokinetic nystagmus (OKN) in humans. We studied regional cerebral blood flow in eight volunteers during reflexive induction of OKN by a pattern of dots moving unidirectionally (toward the left side). We used two control conditions, with subjects passively viewing either stationary or incoherently moving dots. This paradigm was designed in order to differentiate the OKN-related activations from blood flow changes related to visual motion. When compared with the stationary condition, OKN activated a set of occipital areas known to be sensitive to visual motion. Bilateral activation was found in the striate cortex (V1) and the parieto-occipital fissure, while area V5, the intraparietal sulcus, and the pulvinar were activated only in the left hemisphere. When compared with incoherent motion, OKN activated the V1 and the parieto-occipital fissure bilaterally and the right lingual gyrus, while a signal decrease was observed in the V5 region in both hemispheres. No significant signal changes were found in areas implicated in saccades or in processing vestibular information. These results indicate that processing of OKN-related information is associated with neural activity in a specific set of visual motion areas and suggest that this network can be asymmetrically activated by a strictly unidirectional stimulation. Results are also discussed in terms of the specific kinds of OKN-related information processing subserved by each area in this network. Received: 23 June 1998 / Accepted: 28 December 1998     

正电子断层扫描-PET的图像重建

随着计算机技术的迅速发展，ＰＥＴ图像重建方法得以很大的改进，其研究工作越来越受到人们的重视。特别是对能压制噪声和提高空间分辨率的图像快速重建算法的研究是目前一个热门课题。本文简介了ＰＥＴ图像重建的基本原理与基本方法及其研究与应用现状。此外，对ＰＥＴ的三维重建也做了一些简介。     

Prefrontal control of trace eyeblink conditioning in rabbits (Oryctolagus cuniculus) II: effects of type of unconditioned stimulus (airpuff vs. periorbital shock) and unconditioned stimulus intensity

Previous research has implicated the medial prefrontal cortex (mPFC) in the control of classically conditioned autonomic and somatomotor responses. In eyeblink (EB) classical conditioning prefrontal involvement appears to be limited to paradigms that are more difficult to learn, in that acquisition is slower. These include trace conditioning and discrimination/reversal. Some of this research suggests that the participation of mPFC in classical EB conditioning is related to the intensity or type of unconditioned stimulus (US) employed. In the present two experiments we thus studied the effects of manipulation of periorbital shock intensity as the US in Experiment 1 and in Experiment 2 the intensity of a corneal airpuff as the US on Pavlovian trace EB conditioning. The results indicate that there are optimal intensities of both airpuff and periorbital shock as the US in the demonstration of mPFC control of trace classical EB conditioning.     

The Onset of Contingency Awareness and Electrodermal Classical Conditioning: An Analysis of Temporal Relationships during Acquisition and Extinction

The temporal relationship between the onset of contingency awareness and the onset of discrimination classical conditioning of the skin conductance response was evaluated. Awareness of the CS-UCS contingencies and skin conductance responses were measured trial-by-trial from 60 college student subjects during both acquisition and extinction. In addition, the conditioning paradigm was embedded within a masking task in order to delay the onset of awareness so that preaware and postaware trials could be analyzed. Two skin conductance responses were measured, a short latency first interval response (FIR) and a longer latency second interval response (SIR). Results showed that: 1) the onset of FIR discrimination conditioning began only after subjects indicated awareness of both the positive (CS+) and the negative (CS?) contingencies, 2) concurrent with the onset of this awareness, a) FIR discrimination increased suddenly due to increased responding to CS+ while b) SIR discrimination also increased suddenly for some subjects but gradually developed for others, 3) FIR extinction occurred only among subjects who exhibited expectancy extinction, and was due to decreased responding to CS+. The results are consistent with the interpretation that FIR discrimination is related to the cognitive processing of the CSs’significance, and that SIR discrimination is related to an individual difference variable which was reflected in the rate at which subjects became aware.     

Neural control of fast-regular saccades and antisaccades: an investigation using positron emission tomography

 Regional cerebral blood flow changes related to the performance of two oculomotor tasks and a central fixation task were compared in ten healthy human subjects. The tasks were: (a) performance of fast-regular saccades; (b) performance of voluntary antisaccades away from a peripheral cue; (c) passive maintenance of central visual fixation in the presence of irrelevant peripheral stimulation. The saccadic task was associated with a relative increase in activity in a number of occipitotemporal areas. Compared with both the fixation and the saccadic task, the performance of antisaccades activated a set of areas including: the superior and inferior parietal lobules, the precentral and prefrontal cortex, the cingulate cortex, and the supplementary motor area. The results of the present study suggest that: (a) compared with self-determined saccadic responses the performance of fast regular, reflexive saccades produces a limited activation of the frontal eye fields; (b) in the antisaccadic task the inferior parietal lobes subserve operations of sensory-motor integration dealing with attentional disengagement from the initial peripheral cue (appearing at an invalid spatial location) and with the recomputation of the antisaccadic vector on the basis of the wrong (e.g., spatially opposite) information provided by the same cue. Received: 20 May 1996 / Accepted: 28 January 1997     

Effects of CS–US interval modification on diminution of the unconditioned response in electrodermal classical conditioning

The purpose of this experiment was to study whether interstimulus interval (ISI) modification differentially affects the amplitude of the unconditioned response (UR amp.). Seventy-five volunteer subjects received discrimination training with an interval between conditioned stimulus (CS) and unconditioned stimulus (US; aversive white noise) of 8 s. After the discrimination training phase, subjects exhibiting discriminative control were randomized into three groups that differed according to the ISI, of 1, 5 or 8 s. The subjects of each group were then tested with five presentations of CS+/US. The results demonstrate that the UR showed a greater amplitude when an ISI of 8 s was used than with ISIs of 1 or 5 s. No significant differences were found between the UR amp. of the 1- and 5-s ISI groups. These findings are discussed as a result of a hypothetical experimentally induced blend of the anticipatory CRs with the UR.     

正电子发射断层显像在乳腺癌诊治中的应用

乳腺癌是常见的恶性肿瘤之一,在过去25年中,其发病率增高了10%~15%。但随着临床诊断技术和治疗水平的提高,死亡率呈现下降趋势[1]。乳腺成像技术在临床上的广泛应用对乳腺癌的早期诊断与治疗起着重要作用,尤其是功能影像学技术的开展,可在早期甚至是亚临床期及时发现肿瘤。本文讨     

Effects of Potentially Phobic Conditioned Stimuli on Retention, Reconditioning, and Extinction of the Conditioned Skin Conductance Response

Discriminative classical conditioning of skin conductance responses (SCRs) was studied in 163 college students as a function of four variables: CS type (potentially phobic versus neutral conditioned stimuli), Sex of the subject, Interstimulus interval (ISI) during conditioning (.5 versus 8 s), and Retention interval between conditioning and retention assessment (1 versus 6 months). CS type did not affect acquisition, retention, or reconditioning of the differential conditioned responses. The effect of CS type was highly significant during extinction, with differential SCRs to CS+ and CS- being greater with potentially phobic conditioned stimuli. This was true for both sexes, both the .5-s and the 8-s ISI, and after a 1-month or a 6-month retention interval. Moreover, SCRs conditioned to phobic conditioned stimuli with the .5-s ISI persisted even after subjects' cognitive expectancy of the UCS, which was measured on a trial-by-trial basis, had completely extinguished. The results indicate that the effect of potentially phobic conditioned stimuli on the conditioned skin conductance response is unique to resistance to extinction-they affect not learning but unlearning of the autonomic response.     

Effects of classical conditioning on identification and cortical processing of speech syllables

The present study was designed to examine effects of learned motivational significance on processing of speech syllables in adults using a classical conditioning paradigm. Aversive white noise (unconditioned stimulus) was paired with two exemplars of /ba/ (conditioned stimulus, CS+) occurring near the category boundary of a 10-item /ba/-da/ continuum. Two corresponding /da/ syllables served as the CS- and indicated absence of white noise. High-density electroencephalogram (EEG) was recorded while participants passively listened to the stimuli. Prior to the EEG session and after intermittent conditioning, participants were asked to identify the syllables in a categorical perception task. Analysis of time-locked electrocortical data revealed amplitude modulations of the N2 (248-312 ms) component as a function of acquired stimulus properties (CS+ versus CS-). Over right hemisphere regions, negativity was specifically enhanced for the CS+ during intermittent conditioning. During extinction, this conditioning effect was paralleled by findings in the time-frequency domain, showing greater oscillatory activity in the gamma-band (25-40 Hz) range, 80-120 ms following onset of the CS+ compared with CS-. A similar pattern emerged in a later time segment of 400-600 ms (30-45 Hz). Aversive conditioning was not reflected in superior categorical perception performance. Our data indicate that electrocortical correlates of speech syllable perception are susceptible to changes induced by contingencies. Physiological differences were not manifest in behavioral advantage for a specific stimulus, i.e., the CS+, however. We conclude that training speech categorization by merely enhancing motivational relevance is not effective for conveying behavioral improvement.     

Extinction in fear conditioning: Effects on startle modulation and evaluative self-reports

A basic feature of human evaluative conditioning is that the reported acquired valence of a previously neutral conditioned stimulus (CS) that has been paired with a valenced unconditioned stimulus (US), is resistant to extinction. The present study investigated whether startle modulation, sometimes presented as an index of acquired valence, reflected this basic feature. In a differential fear conditioning paradigm ( n = 38) with an electrocutaneous stimulus as the US, a strong extinction manipulation was conducted by removing the US-electrodes and by extended extinction trials. At the end of extinction, the results corroborated previous findings of evaluative conditioning in that the reported valence for CS+ was still more negative than for CS−, despite disappearance of the differential skin conductance responses. However, startle modulation did not show resistance-to-extinction. Results were discussed in terms of recent conceptualizations of extinction.     

First Interval Skin Conductance Responses: Conditioned or Orienting Responses?

This paper was concerned primarily with whether or not the first interval response in classical skin conductance conditioning can be interpreted as a response which occurs at least in part as a consequence of the pairing of, or contingency between, a conditioned stimulus and an unconditioned stimulus. Based on a context in which classical conditioning is seen strictly as a method of inquiry, not as a process, the problems of various control procedures were discussed. It was concluded that with a simple conditioning paradigm the data available to date are sufficiently confounded with differential habituation rates in control-experimental group comparisons that it is difficult to conclude with assurance that the first-interval response does reflect the contingency between the conditioned stimulus and the unconditioned stimulus. In spite of possible confounding factors, the data obtained in differential conditioning experiments permit the conclusion that the first interval response does reflect stimulus pairing.     

Startle reflex facilitation as a function of classical eyeblink conditioning in humans

I investigated whether classical eyeblink conditioning increases the activating effect of the conditional stimulus (CS) on the relevant alpha motoneuron pool in the facial nucleus. The activating effect was measured by the reflex modification method, where startle reflexes, sharing the facial nerve motor pathway with conditional and unconditional eyeblink reflexes, were elicited in the presence of reinforced and nonreinforced CSs (CS+ and CS?). To reduce influences of conditional arousal on startle, a weak airpuff to the eye was used as unconditional stimulus and relatively short stimulus onset asynchronies (SOAs) of 300 and 600 ms were used in three startle tests presented while conditioning was in progress. Two groups (N= 72) received 100% or 0% reinforcement (Groups 100 and 0) of a tone CS+. The CS? was not reinforced. Three startle tests, consisting of acoustic startle probes presented alone and after CS+ and CS? onset, were conducted early, middle, and late in conditioning. Results showed increased startle reflex facilitation after CS+ onset in the late startle test in Group 100, indicating that startle increased as a function of classical conditioning. Although reflex facilitation at the 300-ms SOA in Group 100 is consistent with the hypothesis that CS presentations activated motoneurons in the facial nucleus, the present study cannot itself definitively support this hypothesis. Reflex facilitation at the 600-ms SOA in Group 100 could be influenced by conditional arousal.