Motivational engagement in Parkinson's disease: Preparation for motivated action.

The current study investigated whether motivational dysfunction in Parkinson's patients is related to a deficit in preparing for motivated behavior. Based on previous studies, it was hypothesized that PD patients would show reduced preparation for action specifically when faced with threat (of loss) and that reduced action preparation would relate to self-report of apathy symptoms. The study measured an electrocortical correlate of preparation for action (CNV amplitude) in PD patients and healthy controls, as well as defensive and appetitive activation during emotional perception (LPP amplitude). The sample included 18 non-demented PD patients (tested on dopaminergic medications) and 15 healthy controls who responded as quickly as possible to cues signaling threat of loss or reward, in which the speed of the response determined the outcome. Results indicated that, whereas PD patients showed similar enhanced action preparation with the addition of incentives to controls, PD patients showed generally reduced action preparation, evidenced by reduced CNV amplitude overall. Results suggest that PD patients may have behavioral issues due to globally impaired action preparation but that this deficit is not emotion-specific, and movement preparation may be aided by incentive in PD patients.

Emotion, motivation, and anxiety: brain mechanisms and psychophysiology.

The organization of response systems in emotion is founded on two basic motive systems, appetitive and defensive. The subcortical and deep cortical structures that determine primary motivated behavior are similar across mammalian species. Animal research has illuminated these neural systems and defined their reflex outputs. Although motivated behavior is more complex and varied in humans, the simpler underlying response patterns persist in affective expression. These basic phenomena are elucidated here in the context of affective perception. Thus, the research examines human beings watching uniquely human stimuli--primarily picture media (but also words and sounds) that prompt emotional arousal--showing how the underlying motivational structure is apparent in the organization of visceral and behavioral responses, in the priming of simple reflexes, and in the reentrant processing of these symbolic representations in the sensory cortex. Implications of the work for understanding pathological emotional states are discussed, emphasizing research on psychopathy and the anxiety disorders.

Neuroanatomical correlates of pleasant and unpleasant emotion.

Substantial evidence suggests that a key distinction in the classification of human emotion is that between an appetitive motivational system association with positive or pleasant emotion and an aversive motivational system associated with negative or unpleasant emotion. To explore the neural substrates of these two systems, 12 healthy women viewed sets of pictures previously demonstrated to elicit pleasant, unpleasant and neutral emotion, while positron emission tomographic (PET) measurements of regional cerebral blood flow were obtained. Pleasant and unpleasant emotions were each distinguished from neutral emotion conditions by significantly increased cerebral blood flow in the vicinity of the medial prefrontal cortex (Brodmann's area 9), thalamus, hypothalamus and midbrain (P < 0.005). Unpleasant was distinguished from neutral or pleasant emotion by activation of the bilateral occipito-temporal cortex and cerebellum, and left parahippocampal gyrus, hippocampus and amygdala (P < 0.005). Pleasant was also distinguished from neutral but not unpleasant emotion by activation of the head of the left caudate nucleus (P < 0.005). These findings are consistent with those from other recent PET studies of human emotion and demonstrate that there are both common and unique components of the neural networks mediating pleasant and unpleasant emotion in healthy women.

Emotion, attention, and the startle reflex.

This theoretical model of emotion is based on research using the startle-probe methodology. It explains inconsistencies in probe studies of attention and fear conditioning and provides a new approach to emotional perception, imagery, and memory. Emotions are organized biphasically, as appetitive or aversive (defensive). Reflexes with the same valence as an ongoing emotional state are augmented; mismatched reflexes are inhibited. Thus, the startle response (an aversive reflex) is enhanced during a fear state and is diminished in a pleasant emotional context. This affect-startle effect is not determined by general arousal, simple attention, or probe modality. The effect is found when affects are prompted by pictures or memory images, changes appropriately with aversive conditioning, and may be dependent on right-hemisphere processing. Implications for clinical, neurophysiological, and basic research in emotion are outlined.

Emotion, novelty, and the startle reflex: habituation in humans.

Previous research with both animal and human subjects has shown that startle reflex magnitude is potentiated in an aversive stimulus context, relative to responses elicited in a neutral or appetitive context. In the present experiment, the same pleasant, unpleasant, and neutral picture stimuli were repeatedly presented to human subjects. Startle reflex habituation was assessed in each stimulus context and was compared with the habituation patterns of heart rate, electrodermal, and facial corrugator muscle responses. All systems showed initial differentiation among affective picture contents and general habituation over trials. The startle reflex alone, however, continued to differentiate among pleasant, neutral, and unpleasant pictures throughout the presentation series. These results suggest that (a) the startle probe reflex is relatively uninfluenced by stimulus novelty, (b) the startle modulatory circuit (identified with amygdala-reticular connections in animals) varies systematically with affective valence, and (c) the modulatory influence is less subject to habituation than is the obligatory startle pathway or responses in other somatic and autonomic systems.

Startle potentiation: shock sensitization, aversive learning, and affective picture modulation.

This study investigated the size of, and relationship between, different modulatory effects of aversive stimulation on the acoustic startle reflex. This reflex is potentiated by shock exposure and associative shock conditioning (in animals and human volunteers) and unpleasant pictures (in human volunteers). In this study, dramatic sensitization of the probe-startle response was observed after shock exposure but not after a control task. Magnitude of sensitization was significantly larger than associative shock conditioning and picture modulation effects (also significant). Sensitization and conditioning scores showed modest, significant correlations with one another but not with picture modulation scores, consistent with animal data showing that partially overlapping brain mechanisms (i.e., amygdaloid-reticular projections) mediate these effects. The present results also indicate that sensitization of startle in human volunteers is a relatively more robust defensive response to aversive stimulation.

Cumulative mean change procedure: application to a comparative trial of venlafaxine, imipramine, and placebo in the treatment of major depression.

1. A simple summary measure--namely, cumulative mean change (CMC)--is proposed for analyzing incomplete repeated measures in clinical settings. 2. A simple test statistic that uses the correlation between subject responses was derived and applied to a study comparing an investigational antidepressant, venlafaxine, with imipramine and placebo. 3. The global fashion in which CMC captured all data confirmed the efficacy advantage of venlafaxine over the two control agents.

Emotion in the criminal psychopath: startle reflex modulation.

Startle-elicited blinks were measured during presentation of affective slides to test hypotheses concerning emotional responding in psychopaths. Subjects were 54 incarcerated sexual offenders divided into nonpsychopathic, psychopathic, and mixed groups based on file and interview data. Consistent with findings for normal college students, nonpsychopaths and mixed subjects showed a significant linear relationship between slide valence and startle magnitude, with startle responses largest during unpleasant slides and smallest during pleasant slides. This effect was absent in psychopaths. Group differences in startle modulation were related to affective features of psychopathy, but not to antisocial behavior per se. Psychopathy had no effect on autonomic or self-report responses to slides. These results suggest an abnormality in the processing of emotional stimuli by psychopaths that manifests itself independently of affective report.

The psychopath as observer: emotion and attention in picture processing.

This study extended prior work showing abnormal affect-startle modulation in psychopaths. Male prisoners viewed specific categories of pleasant (erotic or thrilling) and unpleasant (victim or direct threat) slide pictures, along with neutral pictures. Acoustic startle probes were presented early (300 and 800 ms) and late (1,800, 3,000, and 4,500 ms) in the viewing interval. At later times, nonpsychopaths showed moderate and strong reflex potentiation for victim and threat scenes, respectively. For psychopaths, startle was inhibited during victim scenes and only weakly potentiated during threat. Psychopaths also showed more reliable blink inhibition across pleasant contents than nonpsychopaths and greater heart rate orienting to affective pictures overall. These results indicate a heightened aversion threshold in psychopaths. In addition, deficient reflex modulation at early times suggested a weakness in initial stimulus evaluation among psychopaths.

Emotional learning, hedonic change, and the startle probe.

A multiple-response analysis of aversive learning was conducted in human subjects. For each subject, two pictorial stimuli were presented--one paired with electric shock. After training, the magnitude of the acoustic startle eyeblink reflex elicited in the context of the shocked picture increased dramatically and was significantly larger than for reflexes elicited during the nonshocked stimulus. Five different picture contents were tested in separate groups: Reflex potentiation was larger for pictures rated as pleasant than pictures rated as unpleasant. Conditioned responses were also evident for skin conductance, heart rate, and affective judgments. Different systems reflected different aspects of the acquired fear response: Conductance change covaried with arousal, and startle probe magnitude varied with affective valence (pleasure). The neurophysiological implications of the data are elucidated, and parallels drawn between animal and human subjects findings.

Brain potentials in affective picture processing: covariation with autonomic arousal and affective report.

Emotionally arousing picture stimuli evoked scalp-recorded event-related potentials. A late, slow positive voltage change was observed, which was significantly larger for affective than neutral stimuli. This positive shift began 200-300 ms after picture onset, reached its maximum amplitude approximately 1 s after picture onset, and was sustained for most of a 6-s picture presentation period. The positive increase was not related to local probability of content type, but was accentuated for pictures that prompted increased autonomic responses and reports of greater affective arousal (e.g. erotic or violent content). These results suggest that the late positive wave indicates a selective processing of emotional stimuli, reflecting the activation of motivational systems in the brain.

Food deprivation and emotional reactions to food cues: implications for eating disorders.

Two studies examined emotional responding to food cues. In experiment 1, normal college students were assigned to 0-, 6- or 24-h of food deprivation prior to presentations of standard emotional and food-related pictures. Food deprivation had no impact on responses elicited by standard emotional pictures. However, subjective and psychophysiological reactions to food pictures were affected significantly by deprivation. Importantly, food-deprived subjects viewing food pictures showed an enhanced startle reflex and increased heart rate. Experiment 2 replicated the food deprivation effects from experiment 1, and examined participants reporting either a habitual pattern of restrained (anorexia-like) or binge (bulimia-like) eating. Food-deprived and binge eater groups showed startle potentiation to food cues, and rated these stimuli as more pleasant, relative to restrained eaters and control subjects. The results are interpreted from the perspective that startle modulation reflects activation of defensive or appetitive motivation. Implications of the data for understanding eating disorders are considered.

Emotion and motivation I: defensive and appetitive reactions in picture processing.

Emotional reactions are organized by underlying motivational states--defensive and appetitive--that have evolved to promote the survival of individuals and species. Affective responses were measured while participants viewed pictures with varied emotional and neutral content. Consistent with the motivational hypothesis, reports of the strongest emotional arousal, largest skin conductance responses, most pronounced cardiac deceleration, and greatest modulation of the startle reflex occurred when participants viewed pictures depicting threat, violent death, and erotica. Moreover, reflex modulation and conductance change varied with arousal, whereas facial patterns were content specific. The findings suggest that affective responses serve different functions-mobilization for action, attention, and social communication-and reflect the motivational system that is engaged, its intensity of activation, and the specific emotional context.

Emotion and motivation II: sex differences in picture processing.

Adhering to the view that emotional reactivity is organized in part by underlying motivational states--defensive and appetitive--we investigated sex differences in motivational activation. Men's and women's affective reactions were measured while participants viewed pictures with varied emotional and neutral content. As expected, highly arousing contents of threat, mutilation, and erotica prompted the largest affective reactions in both men and women. Nonetheless, women showed a broad disposition to respond with greater defensive reactivity to aversive pictures, regardless of specific content, whereas increased appetitive activation was apparent for men only when viewing erotica. Biological and sociocultural factors in shaping sex differences in emotional reactivity are considered as possible mediators of sex differences in emotional response.

Remembering pictures: pleasure and arousal in memory.

Incidental memory performance for pictures that varied along the affective dimensions of pleasantness and arousal was assessed. For both an immediate and delayed (1 year later) free-recall task, only the arousal dimension had a stable effect on memory performance: Pictures rated as highly arousing were remembered better than low-arousal stimuli. This effect was corroborated in a speeded recognition test, in which high-arousal materials encoded earlier in the experiment produced faster reaction times than their low-arousal counterparts. Pleasantness affected reaction time decisions only for pictures not encoded earlier. These results suggest that whereas both the dimensions of pleasantness and arousal are processed at initial encoding, long-term memory performance is mainly affected by arousal.

Measuring emotion: the Self-Assessment Manikin and the Semantic Differential.

The Self-Assessment Manikin (SAM) is a non-verbal pictorial assessment technique that directly measures the pleasure, arousal, and dominance associated with a person's affective reaction to a wide variety of stimuli. In this experiment, we compare reports of affective experience obtained using SAM, which requires only three simple judgments, to the Semantic Differential scale devised by Mehrabian and Russell (An approach to environmental psychology, 1974) which requires 18 different ratings. Subjective reports were measured to a series of pictures that varied in both affective valence and intensity. Correlations across the two rating methods were high both for reports of experienced pleasure and felt arousal. Differences obtained in the dominance dimension of the two instruments suggest that SAM may better track the personal response to an affective stimulus. SAM is an inexpensive, easy method for quickly assessing reports of affective response in many contexts.

The fear potentiated startle effect. Blink reflex modulation as a result of classical aversive conditioning.

A differential conditioning study examined whether an acoustic startle probe, presented during extinction of an aversively conditioned visual stimulus, potentiated the reflex eyeblink response in humans and whether this potentiation varied with the change in affective valence of the conditioned stimulus. Sixty college students were randomly assigned to view a series of two slides, depicting either unpleasant/highly arousing, unpleasant/moderate arousing, neutral/calm, pleasant/moderate arousing or pleasant/highly arousing scenes and objects (duration: 8 sec). During preconditioning (8 trials) and extinction (24 trials) acoustic startle probes (white noise bursts [50 ms; 95 dBA] were administered during and between slide presentation). During acquisition (16 trials) CS+ was reinforced by an electric shock. Startle response magnitudes significantly increased from preconditioning to extinction and were substantially larger to CS+. Conditioned startle reflex augmentation linearly increased with the pleasantness of the slides. Furthermore, subjects showed a greater post-conditioning increase of judged aversiveness to slides that they had previously reported to be more pleasant, exactly paralleling the startle reflex results.

The late positive potential, emotion and apathy in Parkinson's disease.

Parkinson's disease is associated with emotional changes including depression, apathy, and anxiety. The current study investigated emotional processing in non-demented individuals with Parkinson disease (PD) using an electrophysiological measure, the centro-parietal late positive potential (LPP). Non-demented patients with Parkinson's disease (n=17) and healthy control participants (n=16) viewed pleasant, neutral, and unpleasant pictures while EEG was recorded from a 64-channel geodesic net. The Parkinson patients did not differ from controls in terms of early electrophysiological components that index perceptual processing (occipital P100, N150, P250). Parkinson patients, however, showed reduced LPP amplitude specifically when viewing unpleasant, compared to pleasant, pictures as well as when compared to controls, consistent with previous studies suggesting a specific difference in aversive processing between PD patients and healthy controls. Importantly, LPP amplitude during unpleasant picture viewing was most attenuated for patients reporting high apathy. The data suggest that apathy in PD may be related to a deficit in defensive activation, and may be indexed cortically using event-related potentials.

Emotion and ocular responses in Parkinson's disease.

Parkinson's disease (PD) is a neurodegenerative disease that affects motor, cognitive, and emotional functioning. Previous studies reported reduced skin conductance responses in PD patients, compared to healthy older adults when viewing emotionally arousing pictures. Attenuated skin conductance changes in PD may reflect peripheral autonomic dysfunction (e.g., reduced nerve endings at the sweat gland) or, alternatively, a more central emotional deficit. The aim of the current study was to investigate a second measure of sympathetic arousal-change in pupil dilation. Eye movements, a motor-based correlate of emotional processing, were also assessed. Results indicated that pupil dilation was significantly greater when viewing emotional, compared to neutral pictures for both PD patients and controls. On the other hand, PD patients made fewer fixations with shorter scan paths, particularly when viewing pleasant pictures. These results suggest that PD patients show normal sympathetic arousal to affective stimuli (indexed by pupil diameter), but differences in motor correlates of emotion (eye movements).