Concept-based behavioral planning and the lateral prefrontal cortex

Many lines of evidence implicate the lateral prefrontal cortex (LPFC) in the executive control of behavior. In early studies, neuronal activity in this area was thought to retain information about forthcoming movements for a short period until they were executed. However, later studies have stressed its role in the cognitive aspects of behavioral planning, such as behavioral significance, behavioral rules and behavioral goals. The consequence of the intended action (i.e. a change in the state of the target object), rather than the intended movement, is primarily represented in the LPFC during planning. Recent studies show that the LPFC is involved in more abstract aspects of conceptual processes, such as in representing categories of multiple actions at the stage of behavioral planning.     

Visual identification following inferotemporal ablation in the monkey

Nine monkeys took part in two experiments on visual learning and the effect of inferotemporal ablation. The first experiment contrasted lesion effects in two tasks given to separate groups of animals: serial visual reversal learning set with only two visual stimuli in use throughout the experiment, and discrimination learning set with a new pair of visual stimuli for each discrimination problem. Following inferotemporal ablation, the within-reversal learning rate recovered to the normal pre-operative level, while within-problem learning in discrimination learning set remained substantially impaired. This result suggests that inferotemporal ablation does not directly impair visual associative learning, but rather produces a defect in visual identification such that only a small set of familiar stimuli can be correctly identified and associated with reward. The second experiment replicated an earlier experiment in showing that monkeys with inferotemporal ablation could learn at a normal rate to choose between stimuli according to their spatial orientation. A relation between the two types of unimpaired visual learning in the operated animals was suggested and analogies with clinical syndromes were discussed. The experimental results were interpreted within a distributed-trace model of learning, and this interpretation was illustrated and supported by a computer simulation presented in the Appendix.     

Molecular mechanisms of stress-induced prefrontal cortical impairment: implications for mental illness

The symptoms of mental illness often involve weakened regulation of thought, emotion, and behavior by the prefrontal cortex. Exposure to stress exacerbates symptoms of mental illness and causes marked prefrontal cortical dysfunction. Studies in animals have revealed the intracellular signaling pathways activated by stress exposure that induce profound prefrontal cortical impairment: Excessive dopamine stimulation of D1 receptors impairs prefrontal function via cAMP intracellular signaling, leading to disconnection of prefrontal networks, while excessive norepinephrine stimulation of alpha1 receptors impairs prefrontal function via phosphatidylinositol-protein kinase C intracellular signaling. Genetic studies indicate that the genes disrupted in serious mental illness (bipolar disorder and schizophrenia) often encode for the intracellular proteins that serve as brakes on the intracellular stress pathways. For example, disrupted in schizophrenia 1 (DISC1) normally regulates cAMP levels, while regulator of G protein signaling 4 (RGS4) and diacylglycerol kinase (DGKH)-the molecule most associated with bipolar disorder- normally serve to inhibit phosphatidylinositol-protein kinase C intracellular signaling. Patients with mutations resulting in loss of adequate function of these genes likely have weaker endogenous regulation of these stress pathways. This may account for the vulnerability to stress and the severe loss of PFC regulation of behavior, thought, and affect in these illnesses. This review highlights the signaling pathways onto which genetic vulnerability and stress converge to impair PFC function and induce debilitating symptoms such as thought disorder, disinhibition, and impaired working memory.     

Emotional reactivity following surgery to the prefrontal cortex

We aimed to elicit emotion in patients with surgically circumscribed lesions of the prefrontal cortex (PFC) in order to elucidate the precise functional roles in emotion processing of the discrete subregions comprising the ventromedial PFC, including the medial PFC and orbitofrontal cortex (OFC). Three components of emotional reactivity were measured: subjective experience, behaviour, and physiological response. These included measures of self‐reported emotion, observer‐rated facial expression of emotion and measurements of heart rate and heart rate variability (HRV) during film viewing, and a measure of subjective emotional change since surgery. Patients with lesions to the ventromedial PFC demonstrated significant differences compared with controls in HRV during the film clips, suggesting a shift to greater dominance of sympathetic input. In contrast, patients with lesions restricted to the OFC showed significant differences in HRV suggesting reduced sympathetic input. They also showed less facial expression of emotion during positive film clips, and reported more subjective emotional change since surgery compared with controls. This human lesion study is important for refining theoretical models of emotion processing by the ventromedial PFC, which until now have primarily been based on anatomical connectivity, animal lesion, and human functional neuroimaging research. Such theories have implications for the treatment of a wide variety of emotional disorders.     

Measurement variability in infant and maternal behavioral assessment

Evaluations of methodological assessments sometimes show similar, sometimes different patterns of findings reflective of different approaches to the same problem. In this study, frequencies of behaviors of infants and mothers in two cultures based on continuous coding were compared with frequencies based on time-sampling, and resulting patterns of findings were evaluated. Time-sampling and continuous coding give different estimates of absolute frequency of typical infant and maternal behaviors between individuals and between cultural groups. However, time-sampling adequately preserves the relative ranking of infant and mother behaviors among individuals and between cultural groups. If research is concerned with the relative standing of individuals and/or groups on frequency of infant or maternal behavior, then (under specified circumstances) time-sampling and continuous coding yield comparable results.     

Memory for faces dissociates from memory for location following anterior temporal lobectomy

It has been suggested that the right and left mesial temporal lobes are specialized for processing different types of information for long-term memory (LTM). Although findings have been consistent in regard to the dominant role of the left mesial temporal lobe (MTL) in verbal memory, the role of the right MTL in non-verbal memory remains debatable. Given the existence of two cortical pathways specialized for processing different types of visuospatial information, we examined whether memory processing for these two types of information might also be differentially localized. The effect of unilateral anterior temporal lobectomy (ATL) was compared for memory for unfamiliar faces and a novel sequence of spatial locations in 86 ATL patients (left ATL (LATL) = 35; right ATL (RATL) = 51) pre- and post-surgery to examine the contributions of right and left MTL structures to LTM for pattern and spatial information. Memory for spatial location was not related to side of ATL or time of testing. On the facial memory task, RATL patients showed impairments relative to LATL patients prior to surgery, which became magnified after surgery. These results extend the proposed dissociation between an occipitotemporal and an occipitoparietal pathway for processing visuospatial information by demonstrating dissociations in LTM systems for these two types of information. Lesions in the right MTL, adjacent to the cortical structures believed to be specialized for facial recognition, specifically impair the memory encoding of new faces, but not spatial locations.     

Evidence of a role for multiple memory systems in behavioral extinction

The acquisition of learned behavior involves multiple memory systems, and hippocampal system damage impairs cognitive learning while leaving stimulus-response habit learning intact. In view of evidence that extinction also involves new learning, the present experiments examined whether multiple memory systems theory may be applicable to the neural bases of extinction. Adult Long-Evans rats were trained to run in a straight-alley maze for food reward. Twenty-four hours later, rats matched for runway latencies during acquisition received extinction training. In a response extinction condition conducive to habit learning, rats performed a runway approach response to an empty food cup. In a latent extinction condition conducive to cognitive learning, rats were placed at an empty food cup without performing a runway approach response. Prior to daily extinction training, neural activity of the dorsal hippocampus was reversibly inactivated via infusion of bupivacaine (0.75%, 0.5 microl/side). Control rats receiving saline infusions displayed extinction behavior in both the response and latent training conditions. In contrast, rats receiving bupivacaine extinguished normally in the response condition, but did not display latent extinction. The findings (1) confirm that learning underlying extinction of the same overt behavior can occur with or without explicit performance of the previously acquired response, (2) indicate that extinction learning produced by response and latent training procedures can be neuroanatomically dissociated, and (3) suggest that similarly to initial task acquisition, the hippocampus may critically mediate extinction in situations requiring the use of cognitive learning, such as when performance of a previously acquired response habit is prevented.     

Short-term memory in the rhesus monkey: A behavioral analysis of delayed-response performance

This study obtained quantitative data on the bodily orientations of rhesus monkeys in a delayed-response task and determined whether such orientations mediate the correct response in a choice trial. The basic task was a two-key chain schedule with the key leading to food signaled in the initial component. During the subsequent delay interval, the signal was removed, but it was necessary that one of the keys be pressed to advance the schedule to the terminal choice component. The position of the key pressed thus indicated orientation during the delay interval. When the monkeys had free access to the left and right keys, they tended to press the key leading to food throughout the chain schedule components and received food on more than 85% of the trials, even when the delay was extended to 20 seconds. However, when orientation toward the food key was disrupted by forcing the monkeys to press an extraneous center key during the delay, choice performance deteriorated. Requiring the center key presses early, rather than late, in the delay component had a strong disruptive effect. The relation of the results to the mediating coding-response hypothesis is discussed.     

Evidence for a gene-environment interaction in predicting behavioral inhibition in middle childhood

Gene-environment interactions are presumed to shape human behavior during early development. However, no human research has demonstrated that such interactions lead to stable individual differences in fear responses. We tested this possibility by focusing on a polymorphism in the promoter region of the gene for the serotonin transporter (5-HTT). This polymorphism has been linked to many indices of serotonin activity. Specifically, we tested the hypothesis that an interaction between children's 5-HTT status and maternal reports of social support predicts inhibited behavior with unfamiliar peers in middle childhood. Results were consistent with this hypothesis: Children with the combination of the short 5-HTT allele and low social support had increased risk for behavioral inhibition in middle childhood.     

Evidence for a general factor of behavioral activation system sensitivity

Individual differences in one’s propensity to engage the behavioral activation system (BAS) and behavioral inhibition system (BIS) have primarily been studied with Caver and White’s (1994) BIS/BAS scale. Whereas, Carver and White identified the BIS as a unidimensional scale, they identified three separable BAS group factors - drive, fun seeking, and reward responsiveness -which Carver urged against combining into a BAS total score. Despite this, a BAS total score has been used extensively although researchers have yet to test whether a BAS general factor exists and, if so, whether a BAS total score can be interpreted as primarily being a measure of the general factor. The current study observed that the best fitting BAS factor model of those we tested was a hierarchical model with three group facets and a general factor. This model was largely invariant across both sex and race/ethnicity. We show, for the first time, that a general factor accounts for the majority of the variance in BAS total scores. Due to the superior fit of the hierarchical model and variance accounted for by the general factor, we conclude that researchers are psychometrically justified in using a BAS total score.     

Evidence of motor planning in infant reaching behavior

When adults reach for an object, kinematic measures of their approach movement are affected by what they intend to do after grasping it. We examined whether such future intended actions would be reflected in the approach-to-grasp phase of infant reaching. Twenty-one 10-month-old infants were encouraged to either throw a ball into a tub or fit it down a tube. Kinematic measures of the approach phase of the reach toward the ball were obtained using a motion analysis system. Infants, like adults, reached for the ball faster if they were going to subsequently throw it as opposed to using it in the precision action. The perceptual aspects of the ball were the same and cannot account for these kinematic differences. Infants appear to be planning both segments of their actions in advance. Our findings provide evidence for a level of sophistication in infant motor planning not reported before.