Fear conditioning and extinction: Influence of sex and menstrual cycle in healthy humans.

Although sex differences have been demonstrated in behavioral paradigms of fear conditioning, the findings have been inconsistent, and fear extinction has been little studied. The present study investigated the influence of sex and menstrual cycle phase on the recall of fear extinction. Three groups of healthy adult participants were studied: women at 2 different phases of the menstrual cycle (early follicular [early cycle] and late follicular [midcycle]) and men. Participants underwent a 2-day fear conditioning and extinction protocol. The paradigm entailed habituation, fear conditioning, and extinction learning on Day 1 and extinction recall and fear renewal on Day 2. Skin conductance served as the dependent variable. During fear acquisition on Day 1, men showed significantly larger conditioned responses relative to women; early cycle and midcycle women did not differ. No significant group differences were found during extinction learning. On Day 2, men and early cycle women expressed greater extinction memory than midcycle women. These data confirm sex differences in conditioned fear acquisition and suggest that midcycle hormones attenuate extinction recall. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Expression of glutamine:fructose-6-phosphate amidotransferase in human tissues: evidence for high variability and distinct regulation in diabetes

A recent positron emission tomography (PET) study on brain mechanisms in classical, or Pavlovian, conditioning is reviewed. The PET data were compared with skin conductance data recorded off-line. The participants were five men who participated in three different experimental phases. In the first (habituation) phase, a tone was repeated 24 times at random intervals. In the second (acquisition) phase, the tone was paired with a brief shock to the wrist. In the third (extinction) phase, the tone was presented alone again. Statistical parametric mapping analysis of the PET data showed significantly increased activation of the right hemisphere in the orbitofrontal cortex, dorsolateral prefrontal cortex, inferior and superior frontal cortices, and inferior and middle temporal cortices. In the left hemisphere, only Area 19 and the superior frontal cortex showed significant activation. The findings are discussed within a theoretical framework that argues for different brain mechanisms in acquisition and extinction in classical conditioning.     

A comparison of aphasic and non-brain-injured adults on a dichotic CV-syllable listening task

A dichotic CV-syllable listening task was administered to a group of eleven non-brain-injured adults and to a group of eleven adult aphasics. The results of this study may be summarized as follows: 1)The group of non-brain-injured adults showed a slight right ear advantage for dichotically presented CV-syllables. 2)In comparison with the control group the asphasic group showed a bilateral deficit in response to the dichotic CV-syllables, superimposed on a non-significant right ear advantage. 3) The asphasic group demonstrated a great deal of intersubject variability on the dichotic task with six aphasics showing a right ear preference for the stimuli. The non-brain-injured subjects performed more homogeneously on the task. 4) The two subgroups of aphasics, a right ear advantage group and a left ear advantage group, performed significantly different on the dichotic listening task. 5) Single correct data analysis proved valuable by deleting accuracy of report for an examination of trials in which there was true competition for the single left hemispheric speech processor. These results were analyzed in terms of a functional model of auditory processing. In view of this model, the bilateral deficit in dichotic performance of the asphasic group was accounted for by the presence of a lesion within the dominant left hemisphere, where the speech signals from both ears converge for final processing. The right ear advantage shown by one asphasic subgroup was explained by a lesion interfering with the corpus callosal pathways from the left hemisphere; the left ear advantage observed within the other subgroup was explained by a lesion in the area of the auditory processor of the left hemisphere.     

Asymmetric effects of ovarian hormones on hemispheric activity: Evidence from dichotic and tachistoscopic tests.

Previous studies have suggested a role of endogenously cycling ovarian hormones in the modulation of perceptual asymmetries. In the present investigation, participants were given perceptual asymmetry tests including verbal and nonverbal tachistoscopic and dichotic listening tasks during the menstrual and midluteal phases of the menstrual cycle. Salivary levels of estrogen and progesterone were also measured. Analyses of performance on the tachistoscopic tests revealed that left visual field, but not right visual field, accuracy was significantly lower for both verbal and nonverbal tasks at the midluteal phase than at the menstrual phase. Right ear performance on the nonverbal dichotic test was significantly reduced at the midluteal phase. Results suggest suppression of right hemisphere processing areas and possible reduction in callosal transfer efficiency at higher levels of ovarian steroids. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Autonomic responses to shock-associated words in a nonattended message: a failure to replicate

Names of cities were shock associated and then embedded in material presented to the nonattended channel in a dichotic listening and shadowing situation. Despite earlier claims of differential responding to city names in the absence of awareness, no such differential responding was found. A test for conditioning following the dichotic listening task found that the subjects had been conditioned. Postexperimental interviews found that the subjects were aware of the city-shock contingency and had expected to be shocked during the dichotic listening task. Comparisons are made with other studies of galvanic skin responses to unattended words.     

A cardiac measure of cerebral asymmetries in infant auditory perception.

Examined the utility of cardiac habituation response recovery as a method for assessing infant cerebral asymmetries in auditory perception in a dichotic listening test. In a within-Ss design 12 3-mo-old infants were given a series of 4 10-trial tests during which their cardiac responses were habituated to a pair of dichotic speech syllables or music notes. The 10th trial in each test was a test trial on which one ear received its habituation stimulus while the other ear received a novel stimulus of the same type as the habituation pair (speech or music). Both stimulus type and ear receiving the novel stimulus were counterbalanced across tests. Overall, Ss' cardiac responses habituated during the tests and showed differential recovery to the novel stimuli. Specifically, greater response recovery occurred when a novel speech syllable was presented to the right, than to the left ear. Conversely, greater response recovery was found when a novel music note was presented to the left than to the right ear. Results indicate that young infants show a pattern of auditory perceptual asymmetries much like that found in older children and adults. Findings are consistent with the theory that in man the left hemisphere is superior at processing speech and the right hemisphere superior with nonspeech. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Observational fear conditioning in the acquisition and extinction of attentional bias for threat: An experimental evaluation.

Anxious persons show automatic and strategic attentional biases for threatening information. Yet, the mechanisms and processes that underlie such biases remain unclear. The central aim of the present study was to elucidate the relation between observational threat learning and the acquisition and extinction of biased threat processing by integrating emotional Stroop color naming tasks within an observational differential fear conditioning procedure. Forty-three healthy female participants underwent several consecutive observational fear conditioning phases. During acquisition, participants watched a confederate displaying mock panic attacks (UCS) paired with a verbal stimulus (CS+), but not with a second nonreinforced verbal stimulus (CS-). As expected, participants showed greater magnitude electrodermal and verbal-evaluative (e.g., distress, fear) conditioned responses to the CS+ over the CS- word. Participants also demonstrated slower color-naming latencies to CS+ compared to the CS- word following acquisition and showed attenuation of this preferential processing bias for threat following extinction. Findings are discussed broadly in the context of the interplay between fear learning and processing biases for threat as observed in persons suffering from anxiety disorders. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Failure to control prepotent pathways in early stage dementia of the Alzheimer's type: Evidence from dichotic listening.

The authors examined the right ear advantage in a dichotic listening task in healthy aging and very mild and mild stages of Alzheimer's disease. Subjects were simultaneously presented 3 pairs of digits to the left and right ears (e.g., left ear: 4, 3, 1; right ear: 9, 2, 5) for immediate ordered recall. Four lists of triads were presented, varying in presentation rate between digit pairs within a triad (0.5, 1.0, 1.5, 2.0 s). Results indicated that the very mild and mild Alzheimer's groups showed a larger right ear advantage in free recall compared with the healthy controls, indicating a tendency to respond to the prepotent left hemisphere pathway for language processing. Also, the right ear advantage and proportion of switches made during recall were correlated with psychometric measures of frontal lobe function in the mild Alzheimer's group but not in the very mild or healthy control groups. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Evaluative conditioning in the picture–picture paradigm with random assignment of conditioned stimuli to unconditioned stimuli.

Human participants were allocated to 1 of 3 groups. In the conditioning group, each conditioned stimulus (CS)–unconditioned stimulus (UCS) pair was presented 7 times during the acquisition phase. Participants who were assigned to the extinction group saw 5 additional presentations of each CS in isolation after the 7 presentations of each CS–UCS pair. In the latent inhibition group, the CS-only trials were presented before the CS–UCS trials. Overall, a significant evaluative conditioning effect was observed. This effect cannot be dismissed on the basis of the arguments developed by A. P. Field and G. C. L. Davey (see records 1997-42912-009, 1998-11983-008, and 1999-10526-006), and the results thus provide strong evidence for the associative nature of evaluative conditioning. The results are also in line with other findings, which showed that evaluative conditioning is resistant to extinction. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Posttraining effects of amphetamine, chlorpromazine, ketamine, and scopolamine on the acquisition and extinction of the rabbit's conditioned nictitating membrane response.

Four experiments examined whether posttraining deliveries of drugs modified the performance of the rabbit's conditioned nictitating membrane response (NMR) during acquisition and extinction. The results show that ketamine accelerated, but that amphetamine, chlorpromazine, and scopolamine retarded, conditioning when the drugs were injected immediately after the completion of daily training sessions. However, all conditioning effects of the drugs were lost when their deliveries were delayed by 2 hrs after the end of training. During extinction, the only drug that altered conditioned performance was ketamine. Specifically, ketamine retarded the rate of extinction when the drug was given immediately after training. However, delaying ketamine by 2 hrs after training neutralized the drug's influence. These findings indicate that the NMR preparation should be useful in examining how the posttraining delivery of drugs influences associative processes in conditioning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Fear conditioning in panic disorder: Enhanced resistance to extinction.

Enhanced conditionability has been proposed as a crucial factor in the etiology and maintenance of panic disorder (PD). To test this assumption, the authors of the current study examined the acquisition and extinction of conditioned responses to aversive stimuli in PD. Thirty-nine PD patients and 33 healthy control participants took part in a differential aversive conditioning experiment. A highly annoying but not painful electrical stimulus served as the unconditioned stimulus (US), and two neutral pictures were used as either the paired conditioned stimulus (CS+) or the unpaired conditioned stimulus (CS-). Results indicate that PD patients do not show larger conditioned responses during acquisition than control participants. However, in contrast to control participants, PD patients exhibited larger skin conductance responses to CS+ stimuli during extinction and maintained a more negative evaluation of them, as indicated by valence ratings obtained several times throughout the experiment. This suggests that PD patients show enhanced conditionability with respect to extinction. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Timing of extinction relative to acquisition: A parametric analysis of fear extinction in humans.

Fear extinction is a reduction in conditioned fear following repeated exposure to the feared cue in the absence of any aversive event. Extinguished fear often reappears after extinction through spontaneous recovery. Animal studies suggest that spontaneous recovery can be abolished if extinction occurs within minutes of acquisition. However, a limited number of human extinction studies have shown that short interval extinction does not prevent the return of fear. For this reason, we performed an in-depth parametric analysis of human fear extinction using fear-potentiated startle. Using separate single-cue and differential conditioning paradigms, participants were fear conditioned and then underwent extinction either 10 min (Immediate) or 72 hr (Delayed) later. Testing for spontaneous recovery occurred 96 hr after acquisition. In the single cue paradigm, the Immediate and Delayed groups exhibited differences in context, but not fear, conditioning. With differential conditioning, there were no differences in context conditioning and the Immediate group displayed less spontaneous recovery. Thus, the results remain inconclusive regarding spontaneous recovery and the timing of extinction and are discussed in terms of performing translational studies of fear in humans. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Neuronal activity in the medial prefrontal cortex during Pavlovian eyeblink and nictitating membrane conditioning

The present study assessed Pavlovian eyeblink (EB) conditioning, using tones and periorbital shock as the conditioned and unconditioned stimuli (CS and US), and nictitating membrane (NM) conditioning, using tones and airpuffs as the CS and US. During each experiment, CS-evoked changes in multiple-unit activity (MUA) in the medial prefrontal cortex (mPFC) were recorded. Concomitant heart rate (HR) conditioned responses (CRs) were also recorded. A nonassociative control group received explicitly unpaired presentations of the CS and US in each experiment. Increases in both NM and EB CRs occurred over sessions in the paired, but not the unpaired, groups. Decelerative HR CRs also occurred in the eyeshock, but not the airpuff, group. Although tone-evoked increases in neuronal activity were obtained during 10 initial tone-alone presentations in all groups, this activity habituated over trials. CS-evoked increases in neuronal activity also occurred, but this activity was considerably greater in the group that received periorbital shock as the US. During subsequent extinction trials, decreases in tone-evoked neuronal activity occurred in this group, compared with the previous CS/US paired trials. CS-evoked MUA increases were minimal during all except the pretraining phase of the study in the CS/US unpaired control groups and in the paired airpuff group. These findings show that neuronal activity during associative learning occurs in the mPFC during Pavlovian EB, as well as HR conditioning, but this activity apparently reflects an affective component to learning that is only indirectly related to skeletal conditioning.     

Diversity of capsular polysaccharide synthesis gene clusters in Streptococcus pneumoniae

Echoplanar functional magnetic resonance imaging (fMRI) was used in normal human subjects to investigate the role of the amygdala in conditioned fear acquisition and extinction. A simple discrimination procedure was employed in which activation to a visual cue predicting shock (CS+) was compared with activation to another cue presented alone (CS-). CS+ and CS- trial types were intermixed in a pseudorandom order. Functional images were acquired with an asymmetric spin echo pulse sequence from three coronal slices centered on the amygdala. Activation of the amygdala/periamygdaloid cortex was observed during conditioned fear acquisition and extinction. The extent of activation during acquisition was significantly correlated with autonomic indices of conditioning in individual subjects. Consistent with a recent electrophysiological recording study in the rat (Quirk et al., 1997), the profile of the amygdala response was temporally graded, although this dynamic was only statistically reliable during extinction. These results provide further evidence for the conservation of amygdala function across species and implicate an amygdalar contribution to both acquisition and extinction processes during associative emotional learning tasks.     

Emotional Conditioning to Masked Stimuli and Modulation of Visuospatial Attention.

Two studies investigated the effects of conditioning to masked stimuli on visuospatial attention. During the conditioning phase, masked snakes and spiders were paired with a burst of white noise, or paired with an innocuous tone, in the conditioned stimulus (CS)+ and CS- conditions, respectively. Attentional allocation to the CSs was then assessed with a visual probe task, in which the CSs were presented unmasked (Experiment 1) or both unmasked and masked (Experiment 2), together with fear-irrelevant control stimuli (flowers and mushrooms). In Experiment 1, participants preferentially allocated attention to CS+ relative to control stimuli. Experiment 2 suggested that this attentional bias depended on the perceived aversiveness of the unconditioned stimulus and did not require conscious recognition of the CSs during both acquisition and expression. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Naloxone induces multiple effects on aversive Pavlovian conditioning in rabbits.

Five experiments examined the effects of iv naloxone treatment on aversive Pavlovian conditioning of eye-blink and heart-rate responses, and related unconditioned behaviors, in 143 male albino rabbits. Naloxone (NX) treatment before testing attenuated bradycardiac orienting responses to tones used as CSs. NX also attenuated conditioned bradycardia when administered either before or after training sessions, but it potentiated conditioned bradycardia during extinction of discriminative conditioning. NX did not influence acquisition or extinction of discriminative eye-blink conditioning or somatic or cardiac responses to shocks used as UCSs, but it did decrease locomotor activity. NX immediately after training sessions facilitated acquisition of eye-blink responses. It is concluded that NX influences aversive Pavlovian conditioning in more than one way: (a) During training, it appears to alter reception and processing of signals but does not affect subsequent development of somatic responses to the Pavlovian conditioning contingency. (b) After training, NX apparently affects consolidation of both somatic and autonomic conditioning. (c) NX also appears to delay extinction of Pavlovian conditioning; this effect may similarly involve changes in a stimulus-processing mechanism or in memory functions, but it apparently does not involve changes in somatomotor responsivity. (44 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of sex and sex role attributions on the ear advantage in dichotic listening.

The Bem Sex Role Inventory (BSRI) and a dichotic listening task were administered to 30 participants in order to investigate the effect of polar sex (male, female) and spectral sex (masculinity, femininity) on hemispheric interactions. The dichotic pairs consisted of the consonant-vowel syllables Bee, Dee, Gee, Pee, Tee, and Kee. Although overall performance was the same across groups, women demonstrated smaller right ear advantages than men, due primarily to smaller right ear scores. Less masculine men also had smaller right ear advantages than more masculine men, but this difference was due primarily to greater left ear scores. These results were interpreted both in terms of the callosal relay and direct access models of hemispheric processing. Based on these interpretations, it was suggested that sex and sex role attribution have similar, but not identical effects on interhemispheric relations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Delay eyeblink classical conditioning is impaired in Fragile X syndrome.

The authors examined 400 ms delay eyeblink classical conditioning in 20 participants with Fragile X syndrome ages 17 to 77 years, and 20 age-matched, healthy control participants. The participants in the Fragile X group demonstrated impaired learning and abnormal conditioned response timing. Adults with Fragile X (n = 16) were also tested at two successive 12-month follow-up sessions to examine reacquisition and long-term retention. Participants in groups who were older and younger than 45 years demonstrated significant learning during each reacquisition session. Younger participants demonstrated greater retention of the conditioned stimulus/unconditioned stimulus association at each follow-up session than older participants. Fragile X impairs the acquisition and timing of conditioned eyeblink responses, but with repeated training adults with Fragile X syndrome show significant plasticity. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Abstract and effector-specific representations of motor sequences identified with PET

Positron emission tomography was used to identify neural systems involved in the acquisition and expression of sequential movements produced by different effectors. Subjects were tested on the serial reaction time task under implicit learning conditions. In the initial acquisition phase, subjects responded to the stimuli with keypresses using the four fingers of the right hand. During this phase, the stimuli followed a fixed sequence for one group of subjects (group A) and were randomly selected for another group (group B). In the transfer phase, arm movements were used to press keys on a substantially larger keyboard, and for both groups, the stimuli followed the sequence. Behavioral indices provided clear evidence of learning during the acquisition phase for group A and transfer when switched to the large keyboard. Sequence acquisition was associated with learning-related increases in regional cerebral blood flow (rCBF) in a network of areas in the contralateral left hemisphere, including sensorimotor cortex, supplementary motor area, and rostral inferior parietal cortex. After transfer, activity in inferior parietal cortex remained high, suggesting that this area had encoded the sequence at an abstract level independent of the particular effectors used to perform the task. In contrast, activity in sensorimotor cortex shifted to a more dorsal locus, consistent with motor cortex somatotopy. Thus, activity here was effector-specific. An increase in rCBF was also observed in the cingulate motor area at transfer, suggesting a role linking the abstract sequential representations with the task-relevant effector system. These results highlight a network of areas involved in sequence encoding and retrieval.     

Hippocampectomy disrupts the topography of conditioned nictitating membrane responses during reversal learning.

The effects of bilateral hippocampectomy on the topography of conditioned nictitating membrane (NM) responses in 24 male New Zealand white rabbits were examined during 4 learning tasks: 1-tone delay conditioning, unpaired extinction, 2-tone discrimination, and reversal of 2-tone discrimination. Results show that hippocampal ablation altered conditioned NM response topography only during reversal learning and not during the other training paradigms. The shapes of learning curves for hippocampectomized Ss were different from those of controls only during reversal conditioning. Implications for unit-recording studies of hippocampal cellular activity during classical conditioning of the NM response are discussed. (21 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)