Anteromedial Temporal Lobe Damage Blocks Startle Modulation by Fear and Disgust.

The acoustic startle reflex (ASR) is potentiated during negative emotion, but attenuated during positive emotional experience. The modulation of the ASR by fear depends critically on the amygdala. The authors investigated ASR modulation to fearful, disgusting, pleasant, and neutral stimuli in 12 patients with unilateral damage to the anteromedial temporal lobe including the amygdala (6 left, 6 right), 1 patient with bilateral temporal lobe damage including the amygdala, and 12 comparison participants. Both groups with unilateral damage, as well as the subject with bilateral damage, showed a complete lack of ASR potentiation to both fear and disgust stimuli. The findings suggest that potentiation of the ASR by disgust and fear depends on the integrity of the anteromedial temporal lobe. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Pretraining Inactivation of the Caudal Pontine Reticular Nucleus Impairs the Acquisition of Conditioned Fear-Potentiated Startle to an Odor, but Not a Light.

Recent data from developing rats suggest that structures downstream from the amygdala are involved in the acquisition of conditioned fear-potentiated startle (FPS). The authors tested this idea in adult rats by temporarily inactivating the structure critical for FPS, the caudal pontine reticular nucleus (PnC), during fear conditioning. When the conditioned stimulus (CS) was an odor, rats displayed freezing, but not FPS, at test. This effect was not due to a decrease in footshock sensitivity. Further, no savings were evident on retraining. When the CS was a light, inactivation of the PnC had no effect on the acquisition of FPS. Thus, the PnC may be crucial for the acquisition of conditioned FPS to an odor, but not a light. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Lesions of the Dorsal Hippocampus Block Trace Fear Conditioned Potentiation of Startle.

Several studies show that the hippocampus is critical for the memories mediating trace and contextual fear conditioning. This study investigates whether N-methyl-D-aspartate-induced lesions of the dorsal hippocampus made prior to training affect context fear conditioning and trace fear conditioning measured with the fear-potentiated startle. Pretraining excitotoxic lesions of the dorsal hippocampus blocked acquisition of trace fear conditioning to a tone stimulus but did not affect context fear conditioning. These data indicate that without a dorsal hippocampus rats are unable to acquire trace conditioning but can acquire contextual fear when fear is measured by potentiation of the startle response. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Olfactory-Mediated Fear Conditioning in Mice: Simultaneous Measurements of Fear-Potentiated Startle and Freezing.

This study demonstrates that mice display olfactory-cued fear as measured with both freezing and fear-potentiated startle. Following a preconditioning test to measure any unconditioned responses to odor, mice received 5 pairings of a 10-s odor with a 0.25-s, 0.4-mA footshock. The next day, startle and freezing were measured in the presence and absence of the odor. Both fear measures increased after training with amyl acetate (Experiment 1) and acetophenone (Experiment 2). The enhancement of startle did not occur when the same number of odors and shocks were presented in an unpaired fashion (Experiment 3). Furthermore, mice were able to discriminate between an odor paired with shock and a nonreinforced odor (Experiment 4). (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Amygdala Central Nucleus Function Is Necessary for Learning, but Not Expression, of Conditioned Auditory Orienting.

In Pavlovian appetitive conditioning, rats often acquire 2 classes of conditioned responses: those whose form is determined by the reinforcer, and those whose form is determined by characteristics of the conditioned stimulus (CS). Consistent with the results of previous lesion studies, reversible inactivation of amygdala central nucleus function during pairings of an auditory CS with food prevented the acquisition of conditioned orienting responses specific to auditory CSs, whereas food-related conditioned behaviors were acquired normally. Neither inactivation nor posttraining neurotoxic lesions of the central nucleus affected the expression of previously acquired conditioned orienting. Thus, although the central nucleus is critical to the acquisition of information required for conditioned orienting to auditory cues, it is not needed for maintaining this information for later use. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Habituation of the Acoustic and the Tactile Startle Responses in Mice: Two Independent Sensory Processes.

To test whether habituation is specific to the stimulus modality, the authors analyzed cross-habituation between the tactile startle response' (TSR) and the acoustic startle response (ASR). The acoustic artifacts of airpuffs used to elicit the TSR were reduced by using a silencer and were effectively masked by background noise of 90-100 dB sound-pressure level. ASR was elicited by 14-kHz tones. TSR and ASR habituated in DBA and BALB mice: both the TSR and ASR habituated to a greater extent in DBA mice than in BALB mice. In both strains, habituation of the TSR did not generalize to the ASR, and vice versa. From this, the authors concluded that habituation of startle is located in the sensory afferent branches of the pathway. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

D-Cycloserine and the Facilitation of Extinction of Conditioned Fear: Consequences for Reinstatement.

Several recent studies have reported that D-cycloserine (DCS), a partial N-methyl-D-aspartate agonist, facilitates extinction of learned fear in rats. Other studies have shown that representation of the unconditioned stimulus (US) can reinstate learned fear after extinction. This study examined whether this reinstatement effect occurs in Sprague-Dawley rats given DCS at the time of extinction. Results showed that saline-treated rats exhibited the reinstatement effect but DCS-treated rats did not (Experiments 1 and 2). This lack of reinstatement in DCS-treated rats was not due to residual effects of DCS on either US or context processing (Experiment 3). Overall, these results (a) raise questions about the mechanisms underlying DCS facilitation of extinction and (b) suggest that DCS might have substantial practical benefit. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Hippocampus and Pavlovian Fear Conditioning in Rats: Muscimol Infusions Into the Ventral, but Not Dorsal, Hippocampus Impair the Acquisition of Conditional Freezing to an Auditory Conditional Stimulus.

The authors compared the effects of pharmacological inactivation of the dorsal hippocampus (DH) or ventral hippocampus (VH) on Pavlovian fear conditioning in rats. Freezing behavior served as the measure of fear. Pretraining infusions of muscimol, a GABAA receptor agonist, into the VH disrupted auditory, but not contextual, fear conditioning; DH infusions did not affect fear conditioning. Pretesting inactivation of the VH or DH did not affect the expression of conditional freezing. Pretraining electrolytic lesions of the VH reproduced the effects of muscimol infusions, whereas posttraining VH lesions disrupted both auditory and contextual freezing. Hence, neurons in the VH are importantly involved in the acquisition of auditory fear conditioning and the expression of auditory and contextual fear under some conditions. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

5,7-Dihydroxytryptamine Lesions of the Dorsal and Median Raphe Nuclei Interfere With Lithium-Induced Conditioned Gaping, but Not Conditioned Taste Avoidance, in Rats.

Both the dorsal and median raphe nuclei of the midline brainstem region in rats were lesioned with the neurotoxin 5,7-dihydroxytryptamine. Rats were then surgically implanted with intraoral cannulas for fluid delivery and received a single conditioning trial in which 2-min saccharin infusion was followed by either lithium or saline administration. The conditioned gaping seen in the lithium-conditioned rats was significantly attenuated by raphe lesions, indicating that reduction of forebrain serotonin levels interferes with conditioned gaping. However, lesioned rats still expressed comparable conditioned taste avoidance as measured by both the 1- and 2-bottle consumption tests. These results parallel previous pharmacological findings indicating that reduction of serotonin activity interferes with conditioned gaping, but not conditioned taste avoidance. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Blocking, Unblocking, and Overexpectation of Fear: A Role for Opioid Receptors in the Regulation of Pavlovian Association Formation.

Injection of the opioid receptor antagonist naloxone facilitated acquisition of fear to contextual and auditory conditioned stimuli (CSs) in Experiments 1A and 1B. Experiment 2 showed that prior conditioning to a distinctive context blocked conditioning to an auditory CS. Blocking of CS fear was prevented by administrations of naloxone or increases in footshock intensity. Blocking of CS fear was facilitated by decreases in footshock intensity in a naloxone-reversible manner. Experiment 3 showed that compound conditioning of two CSs, each previously and separately paired with shock, produced overexpectation of fear that was reversed by naloxone. These results are consistent with a role for opioid receptors controlling Pavlovian association formation by regulating the discrepancy (A--ΣV) described by R. A. Rescorla and A. R. Wagner (1972). (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Temporal and Qualitative Dynamics of Conditioned Taste Aversion Processing: Combined Generalization Testing and Licking Microstructure Analysis.

The pattern of licking microstructure during various phases of a conditioned taste aversion (CTA) was evaluated. In Experiment 1, rats ingested lithium chloride (LiCl) for 3 trials and were then offered sodium chloride (NaCl) or sucrose on 3 trials. A CTA to LiCl developed and generalized to NaCl but not to sucrose. CTA intake suppression was characterized by reductions in burst size, average ingestion rate, and intraburst lick rate, and increases in brief pauses and burst counts. Compared with previous studies, LiCl licking shifted from a pattern initially matching that for normally accepted NaCl to one matching licking for normally avoided quinine hydrochloride by the end of the 1st acquisition trial. In Experiment 2, a novel paradigm was developed to show that rats expressed CTA generalization within 9 min of their first LiCl access. These results suggest that licking microstructure analysis can be used to assay changes in hedonic evaluation caused by treatments that produce aversive states. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Attention, Heart Rate, and Startle Response During Exposure to Trauma-Relevant Pictures: A Comparison of Recent Trauma Victims and Patients With Posttraumatic Stress Disorder.

Victims of a recent trauma were compared with posttraumatic stress disorder (PTSD) patients and healthy controls to assess whether a specific anxiety response and an attentional bias were evident initially or only in chronic PTSD. Heart rate (HR) and startle response were measured, and a dot-probe task was carried out using trauma-relevant pictures. Severely affected recent trauma victims and chronic PTSD patients showed HR acceleration to trauma-related material, which was the only significant group difference. A bias away from trauma-related material was related to severity of intrusions in recent trauma victims, and the bias toward trauma-related material increased with amplitude of the HR response in PTSD patients. A specific anxiety reaction is present initially in severely affected trauma victims. (PsycINFO Database Record (c) 2010 APA, all rights reserved)