Opposing amygdala and ventral striatum connectivity during emotion identification

Lesion and electrophysiological studies in animals provide evidence of opposing functions for subcortical nuclei such as the amygdala and ventral striatum, but the implications of these findings for emotion identification in humans remain poorly described. Here we report a high-resolution fMRI study in a sample of 39 healthy subjects who performed a well-characterized emotion identification task. As expected, the amygdala responded to THREAT (angry or fearful) faces more than NON-THREAT (sad or happy) faces. A functional connectivity analysis of the time series from an anatomically defined amygdala seed revealed a strong anticorrelation between the amygdala and the ventral striatum/ventral pallidum, consistent with an opposing role for these regions in during emotion identification. A second functional connectivity analysis (psychophysiological interaction) investigating relative connectivity on THREAT vs. NON-THREAT trials demonstrated that the amygdala had increased connectivity with the orbitofrontal cortex during THREAT trials, whereas the ventral striatum demonstrated increased connectivity with the posterior hippocampus on NON-THREAT trials. These results indicate that activity in the amygdala and ventral striatum may be inversely related, and that both regions may provide opposing affective bias signals during emotion identification.     

Distinct contribution of the striatum and cerebellum to motor learning

The striatum and cerebellum have been shown to be key structures of a distributed system for the control of skilled movements. However, the mechanisms under which they operate remain unclear. This study compared the performance of patients with Parkinson's disease (PD) or with cerebellar damage (CE) to that of age-matched controls. Each group performed two visuomotor paradigms: a random variant of the serial reaction time (SRT) task that tested the subject's ability to make efficient stimulus-response associations and an adapted version of the mirror-tracing task that measured their capacity to combine simple movements into complex ones. PD patients with bilateral striatal damage showed an impaired learning profile on the SRT task and a normal facilitation effect in the tracing task, while CE patients showed the reverse pattern. Although further research is needed, the present findings suggest that the striatum and cerebellum are involved in distinct learning mechanisms.     

Differential effect of aging on synaptic plasticity in the ventral and dorsal striatum

Both the ventral and dorsal striatum are involved in various forms of motor, motivational and learning behaviors. Previously, we demonstrated that several striatum-dependent motor and learning behaviors were reduced in mice with increased age. In this study, we investigated the effects of aging on synaptic plasticity in brain slices containing the nucleus accumbens (NAc) or caudate-putamen (CPu), using electrophysiological recordings. We showed that long-term depression (LTD) was reduced or absent in the NAc of aged C57BL/6 mice, whereas the amount of LTD in the CPu of young and aged mice was similar. The LTD induced by 10-Hz stimulation is NMDAR-dependent in the NAc, but NMDAR-independent in the CPu. Our results suggest that NAc LTD may be more sensitive than CPu LTD to the effects of normal aging with a possibility that NMDAR-dependent LTD may be more susceptible to the aging process than non-NMDAR LTD. We also showed that paired-pulse facilitation was diminished in the NAc and CPu in aged mice, suggesting that aging is accompanied by significant decline in presynaptic function in both the ventral and dorsal striata. The age-related reduction in synaptic plasticity may be a cellular mechanism underlying the age-related impairments in striatum-dependent motor and cognitive functions.     

Role of the striatum and the cerebellum in motor skill acquisition

Motor skill acquisition was investigated in patients with Parkinson's disease (PD) or cerebellar dysfunction using two sensory-guided tracking tasks. The subjects had to learn to track a visual target (a square) on a computer screen by moving a joystick under two different conditions. In the unreversed task, the horizontal target movements were semi-predictable and could be anticipated. In the reversed task, the horizontal movements of a pointer which had to be kept within the target square were mirror-reversed to the joystick movements. PD patients showed intact learning of the semi-predictable task and reduced learning of the mirror-reversed task; patients with cerebellar dysfunction showed the opposite pattern. These findings are discussed in relation to the differential contribution of the cerebellum and the striatum to motor skill acquisition: the cerebellum appears to participate in the implementation of anticipatory movements, whereas the striatum may be critically involved in types of motor learning which require a high degree of internal elaboration.     

Role of the striatum and the cerebellum in motor skill acquisition

Motor skill acquisition was investigated in patients with Parkinson's disease (PD) or cerebellar dysfunction using two sensory-guided tracking tasks. The subjects had to learn to track a visual target (a square) on a computer screen by moving a joystick under two different conditions. In the unreversed task, the horizontal target movements were semi-predictable and could be anticipated. In the reversed task, the horizontal movements of a pointer which had to be kept within the target square were mirror-reversed to the joystick movements. PD patients showed intact learning of the semi-predictable task and reduced learning of the mirror-reversed task; patients with cerebellar dysfunction showed the opposite pattern. These findings are discussed in relation to the differential contribution of the cerebellum and the striatum to motor skill acquisition: the cerebellum appears to participate in the implementation of anticipatory movements, whereas the striatum may be critically involved in types of motor learning which require a high degree of internal elaboration.     

Uncertainty-dependent activity within the ventral striatum predicts task-related changes in response strategy

Recent neuroimaging work has demonstrated that the ventral striatum (VS) encodes confidence in perceptual decisions. However, it remains unclear whether perceptual uncertainty can signal the need to adapt behavior (such as by responding more cautiously) and whether such behavioral changes are related to uncertainty-dependent activity within the VS. Changes in response strategy have previously been observed following errors and are associated with both medial frontal cortex (MFC) and VS, two components of the performance-monitoring network. If uncertainty can elicit changes in response strategy (slowing), then one might hypothesize that these changes rely on the performance-monitoring network. In the present study, we investigated the link between perceptual uncertainty and task-related behavioral adaptations (response slowing and accuracy increases), as well as how such behavioral changes relate to uncertainty-dependent activity within MFC and VS. Our participants performed a two-choice perceptual decision-making task in which perceptual uncertainty was reported on each trial while behavioral and event-related functional magnetic resonance imaging data were collected. Analysis of the behavioral data revealed that uncertain (but correct) responses led to slowing on subsequent trials, a phenomenon that was positively correlated with increased accuracy. Critically, post-uncertainty slowing was negatively correlated with the VS activity elicited by uncertain responses. In agreement with previous reports, increases in MFC activation were observed for uncertain responses, although MFC activity was not correlated with post-uncertainty slowing. These results suggest that perceptual uncertainty can serve as a signal to adapt one’s response strategy and that such behavioral changes are closely tied to the VS, a key node in the performance-monitoring network.     

Perception: The interface between cognition and the external world

In contrast to researchers who emphasize the distinction between perception and cognition it is claimed that the perceptual system is closely intertwined with cognition and with our comprehension of the external world. This claim is supported by evidence for two characteristic features of human information processing. One of these features is the use of mental models. If mental models are assumed to be anchored in the perceptual system it will not be necessary to assume a "little man in the head" who reads off the model. Moreover, perceptually based mental models will provide a referential semantics by anchoring mentally represented concepts in the external world. The other feature is the use of perceptually based perspectives in cognition, such as actor or observer perspectives in social cognition. It is concluded that human beings consistently interact within the real world--also when they are just thinking--and that this becomes possible via perceptual processes.     

The short-term storage as a buffer memory between long-term storage and the motor system: A simultaneous-processing model

It is assumed that in a free-recall task the short-term store serves as a memory buffer between the long-term store and a final motor stage of word production. Because of this the retrieval process in long-term store is not hindered by the final motor stage of word production since continued output from the long-term store queues in the buffer for motoric processing. Otherwise a time consuming communication between the two processes would be necessary. A stochastic model of this conceptualization is provided to predict the temporal course of free recall as well as a paradigm in which the contribution of the short-term store in free recall can be studied. The experimental results from this paradigm were used to test the model and to estimate short-term storage capacity on the basis of the time course of free recall. The model predictions were in good agreement with the data and the capacity estimate coincides well with estimates found by totally different methods reported in the literature.     

Self-organizing systems and infant motor development

A dynamical systems approach is used to characterize early motor development. Contemporary theories of motor performance emphasize the self-organizing and autonomous properties of muscle synergies as an example of the dynamical behavior of complex, nonlinear systems. The organization of leg movements in infants is consistent with the dynamical approach. Using this perspective, we view skill development as a multidimensional, emergent phenomenon. The developmental principles derived from motor behavior may apply to other domains.     

Auditory verb perception recruits motor systems in the developing brain: an fMRI investigation

This study investigated neural activation patterns during verb processing in children, using fMRI (functional Magnetic Resonance Imaging). Preschool children (aged 4–6) passively listened to lists of verbs and adjectives while neural activation was measured. Findings indicated that verbs were processed differently than adjectives, as the verbs recruited motor systems in the frontal cortex during auditory perception, but the adjectives did not. Further evidence suggested that different types of verbs activated different regions in the motor cortex. The results demonstrate that the motor system is recruited during verb perception in the developing brain, reflecting the embodied nature of language learning and processing.     

Aggression is associated with greater subsequent alcohol consumption: A shared neural basis in the ventral striatum

Alcohol use and abuse (e.g., binge drinking) are among the most reliable causes of aggressive behavior. Conversely, people with aggressive dispositions (e.g., intermittent explosive disorder) are at greater risk for subsequent substance abuse. Yet it remains unknown why aggression might promote subsequent alcohol use. Both aggressive acts and alcohol use are rewarding and linked to greater activity in neural reward circuitry. Through this shared instantiation of reward, aggression may then increase subsequent alcohol consumption. Supporting this mechanistic hypothesis, participants’ aggressive behavior directed at someone who had recently rejected them, was associated with more subsequent beer consumption on an ad‐lib drinking task. Using functional MRI, both aggressive behavior and beer consumption were associated with greater activity in the bilateral ventral striatum during acts of retaliatory aggression. These results imply that aggression is linked to subsequent alcohol abuse, and that a mechanism underlying this effect is likely to be the activation of the brain's reward circuitry during aggressive acts.

     

The motor side of emotions: investigating the relationship between hemispheres, motor reactions and emotional stimuli

The aim of the present study was to analyze if the left hemisphere preferentially controls flexion responses toward positive stimuli, while the right hemisphere is specialized toward extensor responses to negative pictures. To this end, right-handed subjects had to pull or push a joystick subsequent to seeing a positive or a negative stimulus in their left or right hemifield. Flexion responses were faster for positive stimuli, while negative stimuli were associated with faster extensions responses. Overall, performance was fastest when emotional stimuli were presented to the left visual hemifield. This right hemisphere superiority was especially clear for negative stimuli, while reaction times toward positive pictures showed no hemispheric difference. We did not find any interaction between hemifield and response type. Neither was there a triple interaction between valence, hemifield and response type. We suppose that response dichotomies in humans are not as tightly linked to a hemisphere- and valence-bound reaction type as previously assumed.     

The intrinsic link between motor behavior and temporal cognition

The debate about the cognitive mechanisms behind human temporal processing has raged for decades without a clear resolution. The theory presented here describes a different perspective to the traditional accounts on the issue, namely, that motor behaviors or sequences of motor behaviors provide a means of reproducing time intervals. Evidence behind this perspective includes tapping strategies (exemplified by musicians), counting strategies, and neuropsychological results showing activation of motor areas during temporal cognitive tasks. I propose that motor behaviors aid human timing by offering a set of processes that consistently take a set amount of time to accomplish. Motor behaviors also allow segmentation of larger intervals into smaller intervals that are easier to estimate. I conclude with a discussion of implications of this perspective on temporal cognition.     

The relationship between task difficulty and motor performance complexity

Difficult tasks are commonly equated with complex tasks across many behaviors. Motor task difficulty is traditionally defined via Fitts’ law, using evaluation criteria based on spatial movement constraints. Complexity of data is typically evaluated using non-linear computational approaches. In this project, we investigate the potential to evaluate task difficulty via behavioral (motor performance) complexity in a Fitts-type task. Use of non-linear approaches allows for inclusion of many features of motor actions that are not currently included in the Fitts-type paradigm. Our results indicate that tasks defined as more difficult (using Fitts movement IDs) are not associated with complex motor behaviors; rather, an inverse relationship exists between these two concepts. Use of non-linear techniques allowed for the detection of behavioral differences in motor performance over the entire action trajectory in the presence of action errors and among neutrally co-constrained effectors not detected using traditional Fitts’-type analyses utilizing movement time measures. Our findings indicate that task difficulty may potentially be inferred using non-linear measures, particularly in ecological situations that do not obey the Fitts-type testing paradigm. While we are optimistic regarding these initial findings, further work is needed to assess the full potential of the approach.     

Understanding the dorsal and ventral systems of the human cerebral cortex: beyond dichotomies

Traditionally, characterizations of the macrolevel functional organization of the human cerebral cortex have focused on the left and right cerebral hemispheres. However, the idea of left brain versus right brain functions has been shown to be an oversimplification. We argue here that a top-bottom divide, rather than a left-right divide, is a more fruitful way to organize human cortical brain functions. However, current characterizations of the functions of the dorsal (top) and ventral (bottom) systems have rested on dichotomies, namely where versus what and how versus what. We propose that characterizing information-processing systems leads to a better macrolevel organization of cortical function; specifically, we hypothesize that the dorsal system is driven by expectations and processes sequences, relations, and movement, whereas the ventral system categorizes stimuli in parallel, focuses on individual events, and processes object properties (such as shape in vision and pitch in audition). To test this hypothesis, we reviewed over 100 relevant studies in the human neuroimaging and neuropsychological literatures and coded them relative to 11 variables, some of which characterized our hypothesis and some of which characterized the previous dichotomies. The results of forward stepwise logistic regressions supported our characterization of the 2 systems and showed that this model predicted the empirical findings better than either the traditional dichotomies or a left-right difference.     

The conceptual commonality between impulsiveness as a personality trait and as an ego development stage

This research was an attempt to demonstrate the conceptual commonality between impulsiveness as a trait and as an ego development stage through correlations on measures of both. An Eysenckian measure of broad trait impulsiveness (Imp_B) consisting of four impulsiveness subscales, the Eysenck Personality Questionnaire (EPQ) and the Washington University Sentence Completion Test (WUSCT) of ego development were administered to 62 male students and 101 female students distributed across three different educational levels (Junior High, Senior High and College). Significant correlations between Imp_B and the WUSCT (-0.23 for the males and -0.31 for the females) supported the hypothesized commonality. Correlations between the WUSCT and the four impulsiveness subscales indicated that Narrow Impulsiveness and Risk-taking were more indicative of ego development than Non-planning or Liveliness. Age trends in the patterns of correlations demonstrated that the commonality between trait impulsiveness and ego development was limited to the early stages of ego development. Sex differences on a number of trait measures and on the WUSCT indicated that males lag behind females in ego development during adolescence. It was hypothesized that the aspect of impulsiveness most indicative of ego development was an unsocialized aspect which might be captured by Eysenck's dimension of psychoticism (P). Correlations between P and WUSCT supported this hypothesis (-0.49 for the males and -0.29 for the females). P apparently has more concept commonality with ego development than has trait impulsiveness. Age trends and sex differences in impulsiveness, psychoticism, and aggressiveness were discussed. It was argued that these personality characteristics would be better understood if explored within a developmental framework such as ego development.