Subliminal and supraliminal processing of reward-related stimuli in anorexia nervosa.

BACKGROUND: Previous studies have highlighted the role of the brain reward and cognitive control systems in the etiology of anorexia nervosa (AN). In an attempt to disentangle the relative contribution of these systems to the disorder, we used functional magnetic resonance imaging (fMRI) to investigate hemodynamic responses to reward-related stimuli presented both subliminally and supraliminally in acutely underweight AN patients and age-matched healthy controls (HC). METHODS: fMRI data were collected from a total of 35 AN patients and 35 HC, while they passively viewed subliminally and supraliminally presented streams of food, positive social, and neutral stimuli. Activation patterns of the group × stimulation condition × stimulus type interaction were interrogated to investigate potential group differences in processing different stimulus types under the two stimulation conditions. Moreover, changes in functional connectivity were investigated using generalized psychophysiological interaction analysis. RESULTS: AN patients showed a generally increased response to supraliminally presented stimuli in the inferior frontal junction (IFJ), but no alterations within the reward system. Increased activation during supraliminal stimulation with food stimuli was observed in the AN group in visual regions including superior occipital gyrus and the fusiform gyrus/parahippocampal gyrus. No group difference was found with respect to the subliminal stimulation condition and functional connectivity. CONCLUSION: Increased IFJ activation in AN during supraliminal stimulation may indicate hyperactive cognitive control, which resonates with clinical presentation of excessive self-control in AN patients. Increased activation to food stimuli in visual regions may be interpreted in light of an attentional food bias in AN.

[Executive task performance under deep brain stimulation of the subthalamic nucleus in Parkinson's disease revisited: the modulating influence of apathy, depression and mood]. / Einfluss der Tiefen Hirnstimulation des Nucleus subthalamicus auf exekutive Funktionen bei Patienten mit idiopathischem Parkinson-Syndrom unter Berücksichtigung von Apathie, Depressivität und Stimmung.

We investigated the moderating influence of apathy, depression and transient mood changes on executive functions under best medical treatment and under postoperative stimulation-on and -off conditions in a sample of 33 patients with Parkinson's disease (PD) after deep brain stimulation of the subthalamic nucleus (STN), 33 PD patients with pharmacological treatment only and 34 healthy controls. In comparison to clinical and healthy control groups, DBS patients showed worse executive task performance and also more severe symptoms of depression and apathy. Apathy accounted for differences in stroop interference between groups. The effects of DBS on stroop interference were explained by increased state anxiety in the -off, so that DBS STN had no significant influence on test performance. Consideration of neuropsychiatric symptoms and acute mood changes is an important aspect when evaluating neuropsychological deficits in DBS patients.

L-DOPA administration shifts the stability-flexibility balance towards attentional capture by distractors during a visual search task.

RATIONALE: The cognitive control dilemma describes the necessity to balance two antagonistic modes of attention: stability and flexibility. Stability refers to goal-directed thought, feeling, or action and flexibility refers to the complementary ability to adapt to an ever-changing environment. Their balance is thought to be maintained by neurotransmitters such as dopamine, most likely in a U-shaped rather than linear manner. However, in humans, studies on the stability-flexibility balance using a dopaminergic agent and/or measurement of brain dopamine are scarce. OBJECTIVE: The study aimed to investigate the causal involvement of dopamine in the stability-flexibility balance and the nature of this relationship in humans. METHODS: Distractibility was assessed as the difference in reaction time (RT) between distractor and non-distractor trials in a visual search task. In a randomized, placebo-controlled, double-blind, crossover study, 65 healthy participants performed the task under placebo and a dopamine precursor (L-DOPA). Using 18F-DOPA-PET, dopamine availability in the striatum was examined at baseline to investigate its relationship to the RT distractor effect and to the L-DOPA-induced change of the RT distractor effect. RESULTS: There was a pronounced RT distractor effect in the placebo session that increased under L-DOPA. Neither the RT distractor effect in the placebo session nor the magnitude of its L-DOPA-induced increase were related to baseline striatal dopamine. CONCLUSIONS: L-DOPA administration shifted the stability-flexibility balance towards attentional capture by distractors, suggesting causal involvement of dopamine. This finding is consistent with current theories of prefrontal cortex dopamine function. Current data can neither confirm nor falsify the inverted U-shaped function hypothesis with regard to cognitive control.

Acute alcohol does not impair attentional inhibition as measured with Stroop interference scores but impairs Stroop performance.

RATIONALE: Inhibition is a core executive function and refers to the ability to deliberately suppress attention, behavior, thoughts, and/or emotions and instead act in a specific manner. While acute alcohol exposure has been shown to impair response inhibition in the stop-signal and Go/NoGo tasks, reported alcohol effects on attentional inhibition in the Stroop task are inconsistent. Notably, studies have operationalized attentional inhibition variably and there has been intra- and inter-individual variability in alcohol exposure. OBJECTIVE: This study aimed to examine the acute effects of alcohol on attentional inhibition, considering previous limitations. METHODS: In a single-blind, cross-over design, 40 non-dependent participants with a medium-to-high risk drinking behavior performed a Counting Stroop task (CST) under a baseline and an arterial blood alcohol concentration (aBAC) clamp at 80 mg%. Attentional inhibition was assessed as the alteration of reaction times (RT), error rates (ER), and inverse efficiency scores (IES) between incongruent and congruent trials (interference score). Stroop performance was also assessed regardless of trial-type. RESULTS: Compared to saline, acute alcohol exposure via an aBAC clamp did not affect CST interference scores but increased RTs and IES in both incongruent and congruent trials. CONCLUSIONS: Attentional inhibition (Stroop interference score) was not impaired by clamped moderate alcohol exposure. Acute alcohol impaired Stroop performance evidenced by a general increase in response times. Our findings suggest that response and attentional inhibition do not share the same neurocognitive mechanisms and are affected differently by alcohol. Results could also be explained by automated behaviors known to be relatively unaffected by acute alcohol.

Explicit and implicit learning of event sequences: evidence from event-related brain potentials.

Event-related brain potentials (ERPs) were recorded during a serial reaction time (RT) task, where single deviant items seldom (Experiment 1) or frequently (Experiment 2) replaced 1 item of a repeatedly presented 10-item standard sequence. Acquisition of sequence knowledge was reflected in faster RTs for standard as compared with deviant items and in an enhanced negativity (N2 component) of the ERP for deviant items. Effects were larger for participants showing explicit knowledge in their verbal reports and in a recognition test. The lateralized readiness potential indicated that correct responses were activated with shorter latencies after training. For deviant items, participants with explicit knowledge showed an initial activation of the incorrect but expected response. These findings suggest that the acquisition of explicit and implicit knowledge is reflected in different electrophysiological correlates and that sequence learning may involve the anticipatory preparation of responses.

Neural mechanisms of advance preparation in task switching.

The preparation effect in task switching can be interpreted to reflect cognitive control processes during the interval between task-cue onset and the trial-stimulus onset which support the flexible and rapid configuration of response dispositions. However, it is an open issue what neural processes underlie this effect. In the present study, healthy volunteers underwent functional magnetic resonance imaging (fMRI) while performing a cued task switching paradigm, in which geometric objects had to be classified according to either color or shape. By manipulating the duration of the cue-target-interval (CTI) in the range between 0 and 1500 ms, we were able to dissociate brain activity changes related to the processing of either the cue or the target. A network of frontal and parietal brain areas was activated during advance preparation for the upcoming task independent of whether the task was switched or repeated. The same brain regions also showed increased neural activity in response to targets without advance preparation in contrast to targets with advance preparation which only elicited activations in areas involved in visual processing and motor execution. These findings strongly argue for a 'task-set activation perspective' on advance preparation in task switching [Altmann, E.M., 2004. Advance preparation in task switching: what work is being done? Psychol. Sci. 15, 616-622.], whereas no empirical support could be found for the 'mental gear changing model' of task switching as no significant brain activity changes were observable in association with task switches, switch costs, or the interaction effect of advance preparation on switch costs. Finally, in the light of previous behavioral studies on interference effects of articulatory suppression on task preparation in humans, the present findings are compatible with the assumption that verbalization mechanisms, e.g., the retrieval of a verbal task or goal representation into working memory may be a functional component of advance configuration of task-sets.

Procedural learning in Broca's aphasia: dissociation between the implicit acquisition of spatio-motor and phoneme sequences.

Procedural learning of spatio-motor and phoneme sequences was investigated in patients with Broca's and Wernicke's aphasia and age-matched controls. In Experiment 1, participants performed a standard serial reaction task (SRT) in which they manually responded to a repeating sequence of stimulus locations. Both Broca's and Wernicke's aphasics showed intact sequence learning, as indicated by a reliable response time (RT) cost when the repeating sequence was switched to a random sequence. In Experiment 2, Broca's aphasics and controls performed a new serial search task (SST), which allowed us to investigate the learning of a spatio-motor sequence and a phoneme sequence independently from each other. On each trial, four letters were presented visually, followed by a single auditorily presented letter. Participants had to press one of four response keys to indicate the location of the auditory letter in the visual display. The arrangement of the visual letters was changed from trial to trial such that either the key-presses or the auditory letters followed a repeating pattern, while the other sequence was random. While controls learned both the key-press and the phoneme sequences, Broca's aphasics were selectively impaired in learning the phoneme sequence. This dissociation between learning of spatio-motor and phoneme sequences supports the assumption that partially separable brain systems are involved in procedural learning of different types of sequential structures.