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PubMed2004

Human side preferences in three different whole-body movement tasks.

Animals turn away from the hemisphere with the more active dopamine (DA) system. For humans, a similar relationship has been assumed. However, results from independent studies were obtained from different tasks and indicated different side preferences. To investigate side preferences between different tasks within the same subject, we assessed in 36 healthy research participants (20 women) (1) long-term spontaneous turning (number of 360 degree turns during 20 h), (2) veering (lateral deviations during walking blindfolded straight forward) and (3) stepping (deviations while stepping blindfolded on a given spot) behavior. We observed a left-sided preference for long-term spontaneous turning behavior and no significant side preference for veering and stepping behavior. The absence of consistent side preferences suggests that DA does not equally control lateralized whole-body movements. We propose that visual control enhanced left-sided movement preferences, probably through an enhanced contribution of the right hemisphere to visuo-spatial behavior. Recently, we reported [Neurosci. Lett. 339 (2003) 115] that levodopa supplementation decreases right-sided veering tendencies, while stepping behavior was unaffected by substance intake. We suggest that veering tendencies, which appeared equally pronounced in either direction, are under dopaminergic control as long as attention is directed towards extrapersonal space. Side preferences in lateralized whole-body movement tasks are thus neither comparable between tasks nor within subjects. We conclude that experimental parameters such as visuo-spatial control and spatial task demands (veering is directed to extrapersonal space and stepping to peripersonal space) determine whether or not the DA system is involved.

Adult↗

PubMed2005

Impaired water maze navigation of Wistar rats with retrosplenial cortex lesions: effect of nonspatial pretraining.

Damage to the retrosplenial cortex (RC) impairs the performance of rodents on spatial learning and memory tasks, but the extent of these deficits was previously reported to be influenced by the lesion type, rat strain, and behavioral task used. The present study addressed the issue of whether or not cytotoxic damage to RC impairs place navigation of Wistar rats in the Morris water maze and, if so, whether this is merely attributable to spatial learning deficits or to impaired learning of general (nonspatial) behavioral strategies required to correctly perform this task or both. Behaviorally naive rats with bilateral lesions to RC were significantly impaired relative to sham-lesioned rats both during the period of initial learning of the task and during the later phases of training. In addition, these animals showed enhanced thigmotaxis, indicating that the lesion was associated with considerable abnormalities in nonspatial learning. In contrast, RC-lesioned animals that have been previously familiarized with general task rules in a series of shaping trials did not show more thigmotaxis than did their respective controls. Furthermore, although these rats were still impaired in the middle of the training process, their performance during the period of initial learning as well as by the end of training was found to now be normal. Our results confirm those of earlier studies indicating that RC is important for spatial navigation. The findings herein reported are also consistent with the notion that, in addition to spatial information processing, RC is involved in cognitive processes underlying the ability of subjects to properly respond to general task demands.

Analysis of Variance↗

PubMed2005

Coherence of EMG activity and single motor unit discharge patterns in human rhythmical force production.

The purpose of this study was to examine the modulation of the motor neuronal pool as a function of task dynamics. Specifically, we investigated the effects of task frequency on the single motor unit discharge pattern, electromyogram (EMG) activity and effector force output. Myoelectric activity and effector force were recorded while young adults isometrically abducted their first dorsal interosseus at five sinusoidal targets (0.5 Hz, 1 Hz, 2 Hz, 3 Hz and 4 Hz) and at two force levels (5% and 25% maximum voluntary contraction (MVC)). Individual motor unit spike trains were isolated from the EMG. Auto-spectral and coherence analyses were performed on the force output, EMG and motor unit spike trains. The frequency of maximal coherence between the EMG and force output closely corresponded to the target frequency in all conditions. There was a broadband distribution of power with multiple peaks in the EMG and motor unit spectrums in the 0.5 Hz and 1 Hz targets. However, the EMG and motor unit spectrums in the 2 Hz, 3 Hz and 4 Hz targets were characterized by an increasingly narrower band of activity with one dominant peak that closely corresponded to the target. There is high coherence between EMG output and target force frequency, but the relative contribution of the fast and slow neuromuscular bands are differentially influenced by the task frequency. The rhythmical organization of neuromuscular output in the 0.5 Hz task is relatively broadband and similar to that shown previously for constant level force output. The frequency structure of neuromuscular organization becomes increasingly more narrowband as the frequency of the target increases (2-4 Hz). The modulation of the motor neuronal pool is adaptive and depends on the relative contribution of feedback and feedforward control processes, which are driven by the task demands.

Adult↗

PubMed2004

Effects of pre-training pedunculopontine tegmental nucleus lesions on delayed matching- and non-matching-to-position in a T-maze in rats.

Lesions of the pedunculopontine tegmental nucleus (PPTg) can impair spatial learning tasks, but it is not clear whether those detrimental effects depend on the specific training conditions (for example, number of response choices available) or are secondary to enhanced anxiety. In the present work, rats with either bilateral excitotoxic (ibotenate) lesions of the PPTg (lesion group) or with vehicle infusions (control group) were tested in an elevated plus-maze, in order to measure anxiety-like behaviours and spontaneous locomotion. Subsequently, they were trained in a delayed matching-to-position (DMTP) task in a T-maze (a two-response choice task). After reaching a predefined learning criterion, or after a maximum of 30 training sessions, the animals were trained in a delayed non-matching-to-position (DNMTP) task. Lesioned animals made less grooming episodes, stretch-attend postures and closed arm entries than controls in the elevated plus-maze, suggesting slightly lower anxiety levels. None of the lesioned rats reached the learning criterion for the DMTP, and overall accuracy levels were significantly lower in those rats, compared to controls. In the DNMTP task, lesioned animals showed lower accuracy levels and higher side bias than controls in some of the sessions, but there were no significant differences between the two groups in the proportion of animals reaching the learning criterion. It is concluded that spatial learning deficits induced by damage to the PPTg are not secondary to enhanced anxiety. Instead, those deficits seem to be influenced by several conditions that modify task demands, the number of response choices being only one of such conditions.

Analysis of Variance↗

PubMed2006

Audio-visual dynamic remapping in an endogenous spatial attention task.

Several studies on cross-modal attention showed that remapping processes between sensory modalities occur in the spatial orienting of attention. One hypothesis that accounts for such links is that spatial attention operates upon representations of common locations in the external space. However, convincing evidence only exists for cross-modal links in spatial orienting, leaving the dynamics of these effects unexplored. Four experiments were designed to cope with this issue by having participants being involved in an endogenous orienting task to visual and auditory target stimuli. Targets on invalid trials were embedded into two different kinds of sequences of stimuli: (1) long sequences, wherein three valid trials in one modality preceded the invalid trial in the other modality; (2) short sequences, wherein only one valid trial in one modality preceded the invalid trial in the other modality. Results revealed modality-specific meridian effects in the short sequences, and a significant decrement of the modality-specific meridian effect in the long sequences. The results of these experiments indicate that cross-modal links in visual and auditory spatial attention are based on representations of common locations in the external space across sensory modalities. Moreover, the results strongly support the hypothesis that representations of space are dynamically built and updated according to task demands.

Acoustic Stimulation↗

PubMed2004

Behavior strategy learning in rat: effects of lesions of the dorsal striatum or dorsal hippocampus.

Depending on task demands, there is a growing body of evidence suggesting that the dorsal striatum plays a critical role in not only learning new response strategies but also in the inhibition of pre-existing strategies when a shift in strategy is required. The present experiment examined the effects of lesions of the dorsal striatum or dorsal hippocampus on acquisition of a response-learning rule and a place-learning rule in a Greek Cross version of the Morris water maze. Specifically, adult Long-Evans rats were prepared with either sham lesions or lesions to one of two subcortical areas of the brain considered necessary for processing nondeclarative or declarative memories, the dorsal striatum or the hippocampus, respectively. An analysis of the trial 2 performance pooled across reversals revealed hippocampus lesions induced accelerated acquisition when a response-learning rule was required. A much smaller enhancement effect was observed in dorsal striatum-lesioned animals in the place-learning paradigm. Dorsal hippocampus- and dorsal striatum-lesioned animals were highly impaired on place learning and response learning, respectively. The present results are congruent with a growing body of literature suggesting that different anatomical substrates are involved in the acquisition and maintenance of different types of information, that these processes can occur simultaneously and in parallel, and that the dorsal striatum is necessary for the mediation of stimulus-response learning, while the hippocampus is necessary to mediate the expression of place learning.

Animals↗

PubMed2005

Hypothalamus-pituitary-adrenal system regulation and suicidal behavior in depression.

BACKGROUND: One of the most demanding tasks in psychiatry is to protect patients from suicidal attempts. Preventive strategies could be improved by increasing our knowledge on the pathophysiologic disturbances underlying this behavior. More than 70-80% of suicides occur in the context of depressive disorders, in which dysregulation of the hypothalamus-pituitary-adrenal (HPA) axis is one of the most prominent neurobiological findings. So far data on the involvement of the HPA axis in the pathophysiology of suicidal behavior in depressed patients are controversial. METHODS: In this retrospective study, we administered the combined dexamethasone-suppression/CRH stimulation (Dex/CRH) test to 310 patients with a depressive syndrome characterized at admission for acute and past suicidal behavior within the first 10 days after hospitalization. RESULTS: Suicidal behavior in depressed patients, including past and recent suicide attempts as well as suicidal ideation, was associated with a lower adrenocorticotropin and cortisol response in the combined Dex/CRH test, with lowest hormone levels observed in patients with a recent suicide attempt. DISCUSSION: The findings suggest that suicidal behavior may alter HPA axis regulation in depressed patients. Large-scale prospective studies assessing neuroendocrine changes may help to develop predictors for an early identification of patients at risk for committing suicide.

Adrenocorticotropic Hormone↗

PubMed2006

Brainstem correlates of defensive states in humans.

BACKGROUND: Brainstem auditory evoked potentials (BAEP) reflect the activation of brainstem nuclei in the first milliseconds after presentation of an auditory stimulus. These electrophysiological correlates of neural processing are highly automatic and not influenced by cognitive factors or task demands; however, data from patients with anxiety disorders suggest deviations in the BAEP. It has been hypothesized that these differences reflect heightened activation of structures involved in defensive states, such as the amygdala and locus coeruleus, projecting to the inferior colliculus, one of the brainstem generators of wave V of the BAEP. The present study investigated this possibility by testing BAEP during experimentally induced anxiety in healthy volunteers. METHODS: In this study, BAEP were recorded from healthy normal volunteers under threat of shock, compared with safe conditions. RESULTS: The first experiment (n = 12) showed that shock anticipation increased the amplitude of wave V. A replication experiment (n = 13) confirmed this finding. CONCLUSIONS: Although BAEP are highly robust with respect to attentional manipulations, they are affected by transient activation of the fear system due to threat of shock. This finding indicates that some of the electrophysiological brainstem abnormalities observed in anxiety disorders can be replicated in healthy control subjects by inducing a transient state of anxiety.

Adult↗

PubMed2006

Methodological issues in the quantification of respiratory sinus arrhythmia.

Although respiratory sinus arrhythmia (RSA) is a commonly quantified physiological variable, the methods for quantification are not consistent. This manuscript questions the assumption that respiration frequency needs to be manipulated or monitored to generate an accurate measure of RSA amplitude. A review of recent papers is presented that contrast RSA amplitude with measures that use respiratory parameters to adjust RSA amplitude. In addition, data from two studies are presented to evaluate empirically both the relation between RSA amplitude and respiration frequency and the covariation between RSA frequency and respiration frequency. The literature review demonstrates similar findings between both classes of measures. The first study demonstrates, during spontaneous breathing without task demands, that there is no relation between respiration frequency and RSA amplitude and that respiration frequency can be accurately derived from the heart period spectrum (i.e., frequency of RSA). The second study demonstrates that respiration frequency is unaffected by atropine dose, a manipulation that systematically mediates the amplitude of RSA, and that the tight linkage between the RSA frequency and respiration frequency is unaffected by atropine. The research shows that the amplitude of RSA is not affected by respiration frequency under either baseline conditions or vagal manipulation via atropine injection. Respiration frequency is therefore unlikely to be a concern under these conditions. Research examining conditions that produce (causal) deviations from the intrinsic relation between respiratory parameters and the amplitude of RSA combined with appropriate statistical procedures for understanding these deviations are necessary.

Adolescent↗

PubMed2006

Single versus multiple probe blocks of P300-based concealed information tests for self-referring versus incidentally obtained information.

UNLABELLED: The aim of the present study was to compare two protocols and two information types on detection of concealed knowledge. Four independent groups of subjects were run. Two were tested on probe stimuli of a self-referring (AUTO) nature and two were tested on incidentally acquired details of a mock crime (MOCK). Each pair of groups was run either in a one-probe (1PB) or multiple probe (6PB) block. In the single probe block, which was repeated three times with a different probe on each block, one probe item was randomly repeated multiple times in a Bernoulli series with frequently presented, meaningless or irrelevant items. There was also a rare target item designed to force attention to the stimulus screen. All stimulus types were of the same category within each block. In contrast, in the multiple probe (and category) block, rare probes, rare targets and frequent irrelevant items were repeatedly presented in a Bernoulli series within one block. MAJOR RESULTS: There was a difference in task demand as measured by reaction time between the two protocols (the multiple probe protocol was more demanding), and a difference trend in P300 detection sensitivity between protocols for both information types combined in favor of the 1PB (p<.07). With both protocols combined, there was a trend (p<.07) favoring detection of familiar versus incidentally learned information. In terms of P300 amplitudes, both protocols showed the usual result that P300 to probes was greater than that to irrelevants. Also, as with detection rates, self-referring information was better detected in terms of Probe-Irrelevant P300 amplitude differences than mock crime information, regardless of protocol. There was no effect of time passage across the repeated blocks of the one-probe protocol. Methodological problems with the multiple probe protocol as utilized in most recent publications are discussed.

Adolescent↗

PubMed2004

Major abdominal surgery of the neonate: anaesthetic considerations.

The anaesthetic handling of neonates scheduled for major abdominal surgical procedures is one of the most demanding tasks that can confront an anaesthesiologist. This chapter will review the specific physiological characteristics of the newborn with relevance to anaesthesia and will also provide robust guidelines for the anaesthetic handling of the most frequent diagnoses that need major abdominal surgery during the neonatal period.

Abdomen↗

PubMed2006

The influence of inattention on the neural correlates of scene segmentation.

Numerous experiments show that people are unable to report about unattended information. It is also clear that there is extensive processing in the absence of attention. Here, we study, by using an 'inattentional blindness' paradigm while measuring BOLD responses or MEG to texture displays, to what level of scene segmentation visual information is processed when subjects are not capable of reporting that segregating textures were present. We presented non-segregating and occasionally segregating textures in two different conditions: 1. a condition where subjects were not informed about the presence of the segregating textures while at the same time engaged in a foveal task, resulting in prolonged inattentional blindness and 2. a condition with similar task demands, in which, however, the subjects perceived the segregating textures. BOLD responses from early visual areas (V1, V2, V3, V4) and MEG responses up to 240 ms showed a significant difference between segregating and not segregating textures in both conditions and did not differ from each other, indicating that scene segmentation processes proceed normally during inattention. A difference between the two conditions, and hence an influence of attention, was signaled in area V3a and more parietal MEG sensors around 400 ms.

Adult↗

PubMed2006

Repetitive picture processing: autonomic and cortical correlates.

Emotionally arousing pictures elicit larger late positive potentials (LPPs) than neutral pictures during passive viewing. Moreover, these cortical responses do not rely on voluntary evaluation of the hedonic content and are relatively unaffected by task demands. In this study, we examined modulation of the late positive potential as it varies with stimulus repetition. Three pictures (pleasant, neutral, unpleasant) were presented up to 60 times each. Although the amplitude of the late positive potential during picture viewing declined with stimulus repetition, affective modulation remained intact. On the other hand, autonomic responses (skin conductance and heart rate change) habituated rapidly with stimulus repetition. These findings suggest that while stimulus detection and categorization, reflected in the LPP, is mandatory, autonomic modulation reflects initial orienting responses that habituate rapidly.

Adult↗

PubMed2006

Selective attention to human voice enhances brain activity bilaterally in the superior temporal sulcus.

Regional cerebral blood flow was measured with positron emission tomography (PET) in 10 healthy male volunteers. They heard two binaurally delivered concurrent stories, one spoken by a male voice and the other by a female voice. A third story was presented at the same time as a text running on a screen. The subjects were instructed to attend silently to one of the stories at a time. In an additional resting condition, no stories were delivered. PET data showed that in comparison with the reading condition, the brain activity in the speech-listening conditions was enhanced bilaterally in the anterior superior temporal sulcus including cortical areas that have been reported to be specifically sensitive to human voice. Previous studies on attention to non-linguistic sounds and visual objects, in turn, showed prefrontal activations that are presumably related to attentional control functions. However, comparisons of the present speech-listening and reading conditions with each other or with the resting condition indicated no prefrontal activity, except for an activation in the inferior frontal cortex that was presumably associated with semantic and syntactic processing of the attended story. Thus, speech listening, as well as reading, even in a distracting environment appears to depend less on the prefrontal control functions than do other types of attention-demanding tasks, probably because selective attention to speech and written text are over-learned actions rehearsed daily.

Adult↗

PubMed2006

The effect of visual task difficulty and attentional direction on the detection of acoustic change as indexed by the Mismatch Negativity.

Näätänen's model of auditory processing purports that attention does not affect the MMN. The present study investigates this claim through two different manipulations. First, the effect of visual task difficulty on the passively elicited MMN is assessed. Second, the MMNs elicited by stimuli under attended and ignored conditions are compared. In Experiment 1, subjects were presented with mixed sequences of equiprobable auditory and visual stimuli. The auditory stimuli consisted of standard (80 dB SPL 1000 Hz), frequency deviant (1050 Hz), and intensity deviant (70 dB SPL) tone pips. In a first instance, subjects were instructed to ignore the auditory stimulation and engage in an easy and difficult visual discrimination task (focused condition). Subsequently, they were asked to attend to both modalities and detect visual and auditory deviant stimuli (divided condition). The results indicate that the passively elicited MMN to frequency and intensity deviants did not significantly vary with visual task difficulty, in spite of the fact that the easy and difficult tasks showed a wide variation in performance. The manipulation of the attentional direction (focused vs. divided conditions) did result in a significant effect on the MMN elicited by the intensity, but not frequency, deviant. The intensity MMN was larger at frontal sites when subjects' attention was directed to both modalities as compared to only the visual modality. The attentional effect on the MMN to the intensity deviants only may be due to the specific deviant feature or the poorer perceptual discriminability of this deviant from the standard. Experiment 2 was designed to address this issue. The methods of Experiment 2 were identical to those of Experiment 1 with the exception that the intensity deviant (60 dB SPL) was made to be more perceptible than the frequency deviant (1016 Hz) when compared to the standard stimulus (80 dB SPL 1000 Hz). The results of Experiment 2 also demonstrated that the passively elicited MMN was not affected by large variations in visual task difficulty; this provides convincing evidence that the MMN is independent of visual task demands. Similarly to Experiment 1, the direction of attention again had a significant effect on the MMN. In Experiment 2, however, the frequency MMN (and not the intensity MMN) was larger at frontal sites during divided attention compared to focused visual attention. The most parsimonious explanation of these results is that attention enhances the discriminability of the deviant from the standard background stimulation. As such, small acoustic changes would benefit from attention whereas the discriminability of larger changes may not be significantly enhanced.

Acoustic Stimulation↗

PubMed2006

Electrocortical correlates of control of selective attention to spatial frequency.

In the present study, we investigated control of selective attention to spatial frequency patterns, using a cueing paradigm. Subjects either used the instruction embedded in a word cue to prepare for the upcoming test stimulus (transient attention condition) or used the instruction they received before a block of trials (sustained reference condition), under completely similar stimulus conditions. The pattern of differential cue responses between these two conditions, reflecting top-down attentional control processes, was different between two groups of subjects, effectively canceling each other out. Despite comparable behavioral performance on both cues and targets, one group (n = 4) elicited a fronto-central-parietal positivity, starting 500 ms postcue over frontal and prefrontal areas, later including more central and posterior scalp sites, whereas another group (n = 8) started 400 ms postcue over central sites with a negativity, growing in strength over time and stabilizing over fronto-central sites. Only the group of eight subjects showed some evidence of occipital pretarget biasing activity. Independent of group, source modeling of the attentional control activity showed that attentional control was initiated in anterior, not posterior, parts of the brain. Furthermore, different underlying sources were found for both groups, in addition to signs of differential processing of target stimuli. Possible individual differences in attentional control ability and its relation to usage of different brain areas to deal with the task demands are discussed in more detail.

Adult↗

PubMed2006

Self-paced saccades and saccades to oddball targets in Parkinson's disease.

Patients with Parkinson's disease (PD) manifest difficulty in initiation and execution of movements, particularly when movements are sequential, simultaneous or repetitive. Eye movements are particularly effective in evaluating motor impairments. We utilized a series of saccadic eye movement paradigms to explore the ability of 13 patients with mild-moderate PD and 13 age-matched healthy controls to self-pace saccades between two continuously illuminated targets, before and after an externally cued tracking period, and respond to unexpected changes in task demand. The latter was explored by measuring saccadic responses to unexpected "oddball" targets that appeared during a well-learned reciprocating sequence of saccades, in either the opposite direction to that expected or at twice the anticipated extent. Results indicated that all participants demonstrated a marked increase in saccade amplitudes from the externally cued saccade tracking to the self-paced saccades. Unexpectedly, this difference was magnified in PD patients. Self-paced saccades before externally cueing were also more frequent than requested in the PD group, but timing improved following external cueing. The second key finding was that while patients were able to respond to unexpected changes in target amplitude, performance was more variable (in terms of latency and accuracy) when responding to unexpected changes in target direction. Hence, beneficial effects of external cueing on the timing of self-paced saccades may be mediated through cortical regions, placing less emphasis on striatal regions known to be compromised in PD. Additionally, responding to changes in saccade direction (but not amplitude) may rely on basal ganglia circuitry.

Adult↗

PubMed2007

Event-related power modulations of brain activity preceding visually guided saccades.

To analyze the characteristics of the event-related desynchronization (ERD) and synchronization (ERS) of cortical rhythms during the preparation and execution of a lateralized eye movement, EEG was recorded in normal subjects during a visually guided task. Alpha and beta bands were investigated in three temporal intervals: a sensory period, a delay period and a saccade preparation period time locked with saccade onset. Modulations of ERD/ERS power, coupled with the task, reached the largest amplitudes over the frontal and parieto-occipital regions. Differences of oscillatory activity in the alpha bands revealed an intriguing pattern of asymmetry in parieto-occipital areas. Rightward saccades induced a larger desynchronization with respect to the leftward saccades in the left hemisphere, but not in the right. If representative, these findings are congruent to the established right-hemisphere dominance of the brain areas that direct attention. Moreover differences between the two alpha types emerged in the frontal areas before and during the saccade preparation periods, indicative of differential engagement of these areas depending on the task demands. In conclusion, the present approach shows that planning eye movements is linked with covert orienting of spatial attention and may supply a useful method for studying eye movements and selective attention-related processes.

Adult↗