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An experiment with 42 human Ss used the transswitching procedure to examine tonic stimulus control of phasic and tonic conditioned vasomotor heart rate, and electrodermal reactions. The conditional stimulus (CSs) were photos of angry and friendly human faces, and the unconditional stimulus (US) was a human scream. In one tonic context (blue light), the CSs were paired with the US, in the other context (yellow light), the CSs were presented unpaired. Following acquisition, an extinction series was run with the US omitted during both tonic contexts. Phasic vasomotor and skin conductance reactions differed in the positive and negative tonic segments (stronger in positive). The skin conductance responses also differed during extinction, but the vasomotor responses did not. Tonic differences (following onset of the tonic stimuli) in unelicited skin conductance response frequency, finger pulse volume, and heart rate were also found, although these developed more slowly than the phasic differences. The finger pulse volume tonic difference was greater in extinction than the skin conductance response frequency. There was no effect of the angry-friendly facial expressions, either directly or in interaction with the transswitching effects. The results were interpreted to mean that the transswitching phenomenon is not limited to one another autonomic effector, but is more generalized across the ANS (sympathetic branch). The absence of influence of the facial expressions indicates the relative weakness of the "preparedness" hypothesis in comparison with more influential contextual factors.

Recent experiments have shown that somatic graviceptors exist in humans. Traditionally, extravestibular gravity information has been thought to originate from mechanoreceptors in the joints, muscles and skin. Experiments with normal, paraplegic and nephrectomized subjects revealed that the kidneys and the cardiovascular system are involved in providing truncal gravity information. The present study intends to determine the influence of shifts in body fluid, especially of the distribution of blood along the subjects' spinal (Z-) axis, on the perception of posture. To this end, the distribution of body fluids was altered by means of the technique of lower body negative and positive pressure (LBNP and LBPP). LBNP leads to venous pooling of blood in the legs, whereas LBPP prevents venous blood from pooling, increasing central volume. Changes in blood distribution were measured by segmental impedance cardiography for four body segments: the upper torso (thoracic cavity), lower torso (abdominal and pelvic region), thigh and calf. Seventeen healthy subjects (mean age: 27.3 years) participated in the experiment. They were positioned on the side (right-ear-down head position) on a tilt table which the subjects and the experimenter could tilt via remote control around an axis parallel to the subjects' visual (X-) axis. The experimenter set the initial tilt in total darkness to arbitrary angles while strictly alternating between head-up and head-down tilts. Subjects were then asked to rotate the board until they felt they were in a horizontal posture. Means and variances of eight pairs of settings were taken as a measure of the subjective horizontal posture (SHP). During LBNP (-30 mmHg), subjects perceived being tilted head-up, whereas LBPP (+30 mmHg) led them to feel tilted head-down. The results corroborate the hypothesis of an effect of the blood's mass on graviception and also indicate supplementary contributions of other visceral afferences.

The Necker-Zeno model of bistable perception provides a formal relation between the average duration of meta-stable percepts (dwell times T) of ambiguous figures and two other basic time scales (t(0), ΔT) underlying cognitive processing. The model predicts that dwell times T covary with t(0), ΔT or both. We tested this prediction by exploiting that observers, in particular experienced meditators, can volitionally control dwell times T. Meditators and non-meditators observed bistable Necker cubes either passively or tried to hold their current percept. The latencies of a centro-parietal event-related potential (CPP) were recorded as a physiological correlate of t(0). Dwell times T and the CPP latencies, correlated with t(0), differed between conditions and observer groups, while ΔT remained constant in the range predicted by the model. The covariation of CPP latencies and dwell times, as well as their quadratic functional dependence extends previous psychophysical confirmation of the Necker-Zeno model to psychophysiological measures.

The present study was carried out to determine the inhibitory cortical processes induced by changes in hemodynamics. Previous experiments in humans conducted in our laboratory have shown that there is a close relationship between posture and delta and theta EEG activity. The most pronounced effects were obtained during the 6 degrees head-down tilt (HDT) position. In space medicine the HDT procedure is very frequently employed to simulate micro-gravity and to determine the neurohormonal counter-regulations evoked by the expansion of central volume. Twenty male subjects spent 23 h in bed in 6 degrees HDT and 23 h in 6 degrees HUT (head-up tilt) positions during which EEG (frontal, central, parietal, occipital), startle responses, and reaction-times were measured every 2 h (from 10:00 h till 20:00 h). The effects of cardiovascular deconditioning (CD) regularly occurring after HDT were assessed by examining orthostatic tolerance and the physical work capacity (bicycle ergometry). As expected, 23 h HDT led to more pronounced CD than HUT. Spectral power analyses of EEG revealed increases in delta and theta frequency hands similar to those found during HDT in previous EEG studies. In addition, subjects responded more slowly (S1-S2 reaction-time task) during HDT as compared with HUT bedrest. The influence of HDT on startle response, however, was not in keeping with the initial hypothesis (i.e. dampening of reflex activity). The EEG data and the sensorimotor performance indicated that the body fluid shift towards the thoracic cavity induced by HDT resulted in signs of cortical inhibition. In addition to neural mechanisms, other processes must be postulated which are closely related to the counter-regulation evoked by the varying body positions.

RATIONALE: Biased processing of drug-associated stimuli is believed to be a crucial feature of addiction. Particularly, an attentional bias seems to contribute to the disorder's maintenance. Recent studies suggest differential effects for stimuli associated with the beginning (BEGIN-smoking-stimuli) or the terminal stage of the smoking ritual (END-smoking-stimuli), with the former but not the later evoking high cue-reactivity. OBJECTIVE: The current study investigated the neuronal network underlying an attentional bias to BEGIN-smoking-stimuli and END-smoking-stimuli in smokers and tested the hypothesis that the attentional bias is greater for BEGIN-smoking-stimuli. METHODS: Sixteen non-deprived smokers and 16 non-smoking controls participated in an fMRI study. Drug pictures (BEGIN-smoking-stimuli, END-smoking-stimuli) and control pictures were overlaid with geometrical figures and presented for 300 ms. Subjects had to identify picture content (identification-task) or figure orientation (distraction-task). The distraction-task was intended to demonstrate attentional bias. RESULTS: Behavioral data revealed an attentional bias to BEGIN-smoking-stimuli but not to END-smoking-stimuli in both groups. However, only smokers showed mesocorticolimbic deactivations in the distraction-task with BEGIN-smoking-stimuli. Importantly, these deactivations were significantly stronger for BEGIN- than for END-smoking-stimuli and correlated with the attentional bias score. CONCLUSIONS: Several explanations may account for missing group differences in behavioral data. Brain data suggest smokers using regulatory strategies in response to BEGIN-smoking-stimuli to prevent the elicitation of motivational responses interfering with distraction-task performance. These strategies could be reflected in the observed deactivations and might lead to a performance level in smokers that is similar to that of non-smokers.

An important feature of addiction is the high drug craving that may promote the continuation of consumption. Environmental stimuli classically conditioned to drug-intake have a strong motivational power for addicts and can elicit craving. However, addicts differ in the attitudes towards their own consumption behavior: some are content with drug taking (consonant users) whereas others are discontent (dissonant users). Such differences may be important for clinical practice because the experience of dissonance might enhance the likelihood to consider treatment. This fMRI study investigated in smokers whether these different attitudes influence subjective and neural responses to smoking stimuli. Based on self-characterization, smokers were divided into consonant and dissonant smokers. These two groups were presented smoking stimuli and neutral stimuli. Former studies have suggested differences in the impact of smoking stimuli depending on the temporal stage of the smoking ritual they are associated with. Therefore, we used stimuli associated with the beginning (BEGIN-smoking-stimuli) and stimuli associated with the terminal stage (END-smoking-stimuli) of the smoking ritual as distinct stimulus categories. Stimulus ratings did not differ between both groups. Brain data showed that BEGIN-smoking-stimuli led to enhanced mesolimbic responses (amygdala, hippocampus, insula) in dissonant compared to consonant smokers. In response to END-smoking-stimuli, dissonant smokers showed reduced mesocortical responses (orbitofrontal cortex, subcallosal cortex) compared to consonant smokers. These results suggest that smoking stimuli with a high incentive value (BEGIN-smoking-stimuli) are more appetitive for dissonant than consonant smokers at least on the neural level. To the contrary, smoking stimuli with low incentive value (END-smoking-stimuli) seem to be less appetitive for dissonant smokers than consonant smokers. These differences might be one reason why dissonant smokers experience difficulties in translating their attitudes into an actual behavior change.

Event-related functional magnetic resonance imaging was applied to identify cortical areas involved in maintaining target information in working memory used for an upcoming grasping action. Participants had to grasp with their thumb and index finger of the dominant right hand three-dimensional objects of different size and orientation. Reaching-to-grasp movements were performed without visual feedback either immediately after object presentation or after a variable delay of 2-12 s. The right inferior parietal cortex demonstrated sustained neural activity throughout the delay, which overlapped with activity observed during encoding of the grasp target. Immediate and delayed grasping activated similar motor-related brain areas and showed no differential activity. The results suggest that the right inferior parietal cortex plays an important functional role in working memory maintenance of grasp-related information. Moreover, our findings confirm the assumption that brain areas engaged in maintaining information are also involved in encoding the same information, and thus extend previous findings on working memory function of the posterior parietal cortex in saccadic behavior to reach-to-grasp movements.

Executive working memory operations are related to prefrontal regions in the healthy brain. Moreover, neuroimaging data provide evidence for a functional dissociation of ventrolateral and dorsolateral prefrontal cortex. Most authors either suggest a modality-specific or a function-specific prefrontal cortex organization. In the present study we particularly aimed at the identification of different prefrontal cerebral areas that are involved in executive inhibitory processes during spatial working memory encoding. In an fMRI study (functional magnetic resonance imaging) we examined the neural correlates of spatial working memory processing by varying the amount of executive demands of the task. Twenty healthy volunteers performed the Corsi Block-Tapping test (CBT) during fMRI. The CBT requires the storage and reproduction of spatial target sequences. In a second condition, we presented an adapted version of the Block-Suppression-Test (BST). The BST is based on the original CBT but additionally requires the active suppression of visual distraction within the target sequences. In comparison to the CBT performance, particularly the left dorsolateral prefrontal cortex (BA 9) showed more activity during the BST condition. Our results show that the left dorsolateral prefrontal cortex plays a crucial role for executive controlled inhibition of spatial distraction. Furthermore, our findings are in line with the processing model of a functional dorsolateral-ventrolateral prefrontal cortex organization.