The neuropsychology of hydrocephalus.

The relationship between neuropsychological impairment and hydrocephalus is reviewed and three case studies presented. Current brain imaging technology provides a method for detailed quantification of ventricular expansion and alteration or loss of cortical tissue in hydrocephalus. However, there appears to be little systematic relationship between ventricular size in hydrocephalus and the type or degree of neuropsychological impairment. As a group, hydrocephalic patients do demonstrate a variety of cognitive and perceptual-motor deficits, but there does not appear to be a common diagnostic neuropsychological pattern in hydrocephalus although perceptual-motor/manipulo-spatial deficits appear to predominate. It appears that there is considerable neural plasticity that occurs in some patients with congenital hydrocephalus and much of this functional reorganization may take place at subcortical and subtentorial levels. Clinical guidelines for the neuropsychological assessment of hydrocephalus are given.     

Social learning of fear

Research across species highlights the critical role of the amygdala in fear conditioning. However, fear conditioning, involving direct aversive experience, is only one means by which fears can be acquired. Exploiting aversive experiences of other individuals through social fear learning is less risky. Behavioral research provides important insights into the workings of social fear learning, and the neural mechanisms are beginning to be understood. We review research suggesting that an amygdala-centered model of fear conditioning can help to explain social learning of fear through observation and instruction. We also describe how observational and instructed fear is distinguished by involvement of additional neural systems implicated in social-emotional behavior, language and explicit memory, and propose a modified conditioning model to account for social fear learning. A better understanding of social fear learning promotes integration of biological principles of learning with cultural evolution.     

The role of prefrontal cortex in predictive fear learning

Pavlovian fear conditioning depends on prediction error, or the discrepancy between actual and expected outcomes. We used immunohistochemistry, neuronal tract tracing, and reversible inactivation to study the role of prefrontal cortex and thalamocortical pathways in predictive fear learning. Unexpected, but not expected, conditioned stimulus (CS)-unconditioned stimulus (US) presentations caused increased c-Fos expression in the prefrontal cortex (PFC), midline thalamus, lateral amygdala, as well as retrograde labeled midline thalamic afferents to PFC. Reversible inactivation of dorsomedial PFC, but not infralimbic PFC, prevented the associative blocking of fear learning. These results suggest a role for dorsomedial PFC (dmPFC), and a thalamic → dmPFC pathway, in signaling whether or not aversive events are expected or unexpected and so whether they are to be learned about.     

Sleep and the generalization of fear learning

Fear conditioning is an important survival mechanism, as is the ability to generalize learned fear responses to stimuli that are similar to the original conditioned stimulus. Overgeneralization of fear learning, prominent in many anxiety disorders, is however highly maladaptive. Because sleep is involved in the consolidation of fear learning, and in active processing of information, the present study explored the effect of sleep on generalization of fear learning. Participants watched a random sequence of pictures of a small and a big circle, one of them coupled with an aversive sound. Then, after a delay period containing either a nap or wake, generalization was examined as participants watched the two circles again, together with eight novel circles that gradually varied in size between the former two. Results showed that the fear response increased as a function of similarity to the conditioned response. However, there was no difference in the degree of generalization between the sleep and the wake group.     

The vicarious learning pathway to fear 40 years on

Forty years on from the initial idea that fears could be learnt vicariously through observing other people's responses to a situation or stimulus, this review looks at the evidence for this theory as an explanatory model of clinical fear. First, we review early experimental evidence that fears can be learnt vicariously before turning to the evidence from both primate and human research that clinical fears can be acquired in this way. Finally, we review recent evidence from research on non-anxious children. Throughout the review we highlight problems and areas for future research. We conclude by exploring the likely underlying mechanisms in the vicarious learning of fear and the resulting clinical implications.     

Contribution of the amygdala to learning and performance of conditional fear.

The amygdaloid complex appears to be an essential component in the neural systems mediating some forms of aversive Pavlovian conditioning. The relative contribution of this structure to acquisition and performance during fear conditioning was assessed by making temporary lesions in the amygdala prior to training or retention testing in a single-trial Pavlovian conditioning preparation. Microinjection of lidocaine HCl (5.0%, 1.0 microliters) into the amygdala prior to the presentation of a CS signalling footshock resulted in a significant attenuation of the performance of conditional fear, as indexed by the amount of time rats spent engaged in defensive freezing behavior during the retention session. However, similar treatment with lidocaine prior to the training session, during which the CS and UCS were paired, resulted in only a weak reduction in subsequent responding. Thus, while both acquisition- and performance-related processes take place within the amygdala, it appears that the latter are more sensitive to disruption using the present procedures. These results are discussed in terms of the general role played by this structure in aversive learning and motivational processes.     

The development of fear learning and generalization in 8-13 year-olds

The current study examined developmental changes in fear learning and generalization in 40 healthy 8–13 year‐olds using an aversive conditioning paradigm adapted from Lau et al. [Lau et al. [2008] Journal of the American Academy of Child and Adolescent Psychiatry 47:94–102]. In this task, the conditioned stimuli (CS+/CS?) are two neutral female faces, and the unconditioned stimulus is a fearful, screaming face. The second phase of the study also included a generalization stimulus (GS): a 50% blend of the CS± faces. The eye‐blink startle reflex was utilized to measure defensive responding. Patterns of fear learning and generalization were qualified by child age. Older children demonstrated greater fear learning (i.e., larger startle during CS+ than CS?) than younger children. In addition, older children exhibited the typical pattern of generalization observed in adults, whereas younger children did not. Finally, fear learning also related to contingency awareness; only children who correctly identified the CS+ demonstrated fear‐potentiated startle to the CS+. Clinical implications and future directions are discussed. © 2011 Wiley Periodicals,Inc. Dev Psychobiol 54: 675–684, 2012.     

Context fear learning and renewal of extinguished fear are dissociated in juvenile female rats

Extinction is the decrease in emotion to a cue that was previously associated with an emotionally significant event. It involves repeated presentation of the cue without any consequences. In adult animals, extinguished fear to a cue can return if the cue is presented in a different environment/context to where extinction occurred, referred to as renewal. We have previously reported that developing female, but not male, rats show renewal. This study investigates whether the ability of developing female rats to show renewal is related to their ability in fear conditioning to the context. Additionally, facilitation of context conditioning by weaning previously shown in male rats was tested in developing female rats. In experiment 1, postnatal day 25 (P25) and P18 female rats showed renewal. P25 rats show more fear overall, suggesting a weaker extinction recall in this age. Experiment 2 tested context- and cue-elicited fear either immediately or 24 hr following conditioning. At the immediate test, P18 rats showed less context-fear compared with P25 rats. All rats showed low levels of context-fear at the 24 hr test. There were no age differences in cued fear. Weaning at P21 did not affect context or cue memory in P25 female rats. These findings suggest that the ability to form contextual fear memory is unrelated to the expression of renewal in juvenile female rats.     

The neuropsychology of antisocial personality disorder

BACKGROUND: The literature on executive function in antisocial populations is unclear due to variation in diagnostic criteria and variation in the inclusion of healthy control comparison groups. Some studies suggest prototypical psychopathy is associated with specific deficits in ventromedial prefrontal (VMPFC) function rather than dorsolateral prefrontal (DLPFC). Meta-analytical studies, however, suggest that antisocial personality disorder may be associated with a broader range of executive deficits. This study assessed DLPFC and VMPFC function in antisocial personality disorder subjects and controls using the Cambridge Neuropsychological Test Automated Battery (CANTAB) and a Go/NoGo task respectively. METHODS: All subjects were screened for Axis I pathology, substance misuse and prescribed medication. The performance of 29 subjects with antisocial personality disorder DSM-IV and 20 male right-handed controls (matched for age and IQ) on the neuropsychological test battery was compared. RESULTS: Subjects with antisocial personality disorder displayed impairments on DLPFC executive function tasks of planning ability and set shifting. Impairments were also seen in VMPFC Go/NoGo tasks and in visual memory tasks. CONCLUSIONS: Antisocial personality disorder is associated with a broad range of deficits in DLPFC and VMPFC function. Future studies need to examine relationships between the interpersonal and behavioural components of antisocial personality disorder and neuropsychological function.     

Assessing fear learning via conditioned respiratory amplitude responses

Respiratory physiology is influenced by cognitive processes. It has been suggested that some cognitive states may be inferred from respiration amplitude responses (RAR) after external events. Here, we investigate whether RAR allow assessment of fear memory in cued fear conditioning, an experimental model of aversive learning. To this end, we built on a previously developed psychophysiological model (PsPM) of RAR, which regards interpolated RAR time series as the output of a linear time invariant system. We first establish that average RAR after CS+ and CS− are different. We then develop the response function of fear‐conditioned RAR, to be used in our PsPM. This PsPM is inverted to yield estimates of cognitive input into the respiratory system. We analyze five validation experiments involving fear acquisition and retention, delay and trace conditioning, short and medium CS‐US intervals, and data acquired with bellows and MRI‐compatible pressure chest belts. In all experiments, CS+ and CS− are distinguished by their estimated cognitive inputs, and the sensitivity of this distinction is higher for model‐based estimates than for peak scoring of RAR. Comparing these data with skin conductance responses (SCR) and heart period responses (HPR), we find that, on average, RAR performs similar to SCR in distinguishing CS+ and CS−, but is less sensitive than HPR. Overall, our work provides a novel and robust tool to investigate fear memory in humans that may allow wide and straightforward application to diverse experimental contexts.     

Modeling startle eyeblink electromyogram to assess fear learning

Pavlovian fear conditioning is widely used as a laboratory model of associative learning in human and nonhuman species. In this model, an organism is trained to predict an aversive unconditioned stimulus from initially neutral events (conditioned stimuli, CS). In humans, fear memory is typically measured via conditioned autonomic responses or fear‐potentiated startle. For the latter, various analysis approaches have been developed, but a systematic comparison of competing methodologies is lacking. Here, we investigate the suitability of a model‐based approach to startle eyeblink analysis for assessment of fear memory, and compare this to extant analysis strategies. First, we build a psychophysiological model (PsPM) on a generic startle response. Then, we optimize and validate this PsPM on three independent fear‐conditioning data sets. We demonstrate that our model can robustly distinguish aversive (CS+) from nonaversive stimuli (CS‐, i.e., has high predictive validity). Importantly, our model‐based approach captures fear‐potentiated startle during fear retention as well as fear acquisition. Our results establish a PsPM‐based approach to assessment of fear‐potentiated startle, and qualify previous peak‐scoring methods. Our proposed model represents a generic startle response and can potentially be used beyond fear conditioning, for example, to quantify affective startle modulation or prepulse inhibition of the acoustic startle response.     

Role of conceptual knowledge in learning and retention of conditioned fear

Associating sensory cues with aversive outcomes is a relatively basic process shared across species. Yet higher-order cognitive processes likely contribute to associative fear learning in many circumstances, especially in humans. Here we ask whether fears can be acquired based on conceptual knowledge of object categories, and whether such concept-based fear conditioning leads to enhanced memory representations for conditioned objects. Participants were presented with a heterogeneous collection of images of animals and tools. Objects from one category were reinforced by an electrical shock, whereas the other category was never reinforced. Results confirmed concept-based fear learning through subjective report of shock expectancy, heightened skin conductance responses, and enhanced 24 h recognition memory for items from the conditioned category. These results provide novel evidence that conditioned fear can generalize through knowledge of object concepts, and sheds light on the persistent nature of fear memories and category-based fear responses symptomatic of some anxiety disorders.     

Clinical judgment and decision making in neuropsychology.

We review the literature on clinical judgment and statistical/actuarial prediction both in clinical psychology and in neuropsychology and we attempt to place these findings within the broader context of judgment theory. Current research on judgment in neuropsychology is consistent with research in other areas that documents the limitations of humans as judges and argues for increased utilization of actuarial methods and decision aids. In addition, there are virtually no data suggesting judgmental accuracy is related to experience, acknowledged expertise, or confidence in the accuracy of one's predictions. We attempt to identify judgment practices which contribute to diagnostic error in neuropsychology and we make recommendations that neuropsychologists can use to increase their judgmental accuracy. Research priorities in this area are discussed.