Cognitive Brain Research最新文献

The effects of peripheral vestibular disorders on the direction and distance components of the internal spatial representation were investigated. The ability of Menière's patients to perform path integration was assessed in different situations aimed at differentiating the level of spatial processing (simple versus complex tasks), the available sensory cues (proprioceptive, vestibular, or visual conditions), and the side of the path (towards the healthy versus the lesioned side). After exploring two legs of a triangle, participants were required either to reproduce the exploration path, to follow the reverse path, or to take a shortcut to the starting point of the path (triangle completion). Patients' performances were recorded before unilateral vestibular neurotomy (UVN) and during the time-course of recovery (1 week and 1 month) and were compared to those of matched control subjects tested at similar time intervals. Both the angular and linear path components of the trajectory were impaired for patients compared to controls. However, deficits were restricted to the complex tasks, which required a higher level of spatial processing. Most deficits were maximal 1 week after UVN, and some remained up to the first post-operative month. Spatial representation was differentially impaired according to the available sensory cues: deficits were absent in active locomotor blindfolded condition, appeared in conditions involving visual and vestibular information, and were maximal when visual cues alone were available. Finally, concerning the side of the path, unilateral vestibular loss led to global impairment of the internal spatial representation, yet some asymmetrical spatial performances were observed 1 week after UVN. On the whole, results suggest that the environment experienced by the patients is different after UVN and that a different internal spatial representation is constructed, especially for tasks requiring high levels of spatial processing.

The feedback-related negativity (FRN) is an event-related brain potential component that is elicited by feedback stimuli indicating unfavorable outcomes. Until recently, the FRN has been studied primarily using experimental paradigms in which outcomes appeared to be contingent upon the participants' behavior. The present study further addressed the question whether an FRN can be elicited by outcomes that are not contingent on any preceding choice or action. Participants took part in a simple slot-machine task in which they experienced monetary gains and losses in the absence of responses. In addition, they performed a time estimation task often used to study the FRN and a flanker task known to elicit the error-related negativity. Outcomes in the slot-machine task elicited an FRN-like mediofrontal negativity whose amplitude correlated with the amplitude of the FRN associated with negative feedback in the time estimation task. However, the mediofrontal negativity was observed both for (unfavorable) outcomes that averted a gain and for (favorable) outcomes that averted a loss of money. The results are discussed in the framework of current conceptions of the FRN and related electrophysiological components.

Previous neuroimaging studies devoted to auditory motion processing have shown the involvement of a cerebral network encompassing the temporoparietal and premotor areas. Most of these studies were based on a comparison between moving stimuli and static stimuli placed at a single location. However, moving stimuli vary in spatial location, and therefore motion detection can include both spatial localisation and motion processing. In this study, we used fMRI to compare neural processing of moving sounds and static sounds in various spatial locations in blindfolded sighted subjects. The task consisted of simultaneously determining both the nature of a sound stimulus (pure tone or complex sound) and the presence or absence of its movement. When movement was present, subjects had to identify its direction. This comparison of how moving and static stimuli are processed showed the involvement of the parietal lobules, the dorsal and ventral premotor cortex and the planum temporale during auditory motion processing. It also showed the specific recruitment of V5, the visual motion area. These results suggest that the previously proposed network of auditory motion processing is distinct from the network of auditory localisation. In addition, they suggest that the occipital cortex can process non-visual stimuli and that V5 is not restricted to visual processing.

Altered frontal lobe activity and executive control associated with working memory (WM) dysfunction are recognized as core deficits in schizophrenia. These impairments have been discussed as being associated with deficits in self-regulated action monitoring and anticipatory action plan generation. To study electrophysiological correlates of executive control – specifically action monitoring and action rule switching – under varying WM load, we used a paradigm derived from classic N-back (WM) tasks and requiring monitoring of simple actions. We focused on event-related changes in post-stimulus theta oscillatory activity during varying cognitive and WM demand in healthy controls and schizophrenia patients. The results show significant WM load and rule-switching-related increases of post-stimulus theta amplitude at fronto-central locations in controls. In patients with schizophrenia, there was no such modulation, but – apart from an increased early theta at left temporal locations – generally reduced late theta responses in all tasks and at all locations. Furthermore, the patients with schizophrenia showed significant differences in their error patterns, which imply differences in automation and anticipation of actions between controls and patients. These findings suggest that theta oscillations are involved in mediating frontal lobe activity and functions related to enhanced executive control. We conclude that the patients with schizophrenia showed deficits in acquiring a mental task set which appear to be associated with impairments in action monitoring and task-specific regulation of executive control.

Concepts of higher attention functions distinguish focused and divided attention. The present study investigated whether these mental abilities are mediated by common or distinct neural substrates. In a first experiment, 19 healthy subjects were examined with functional brain imaging (fMRI) while they attended to either one or both of two simultaneously presented visual information streams and responded to repetitive stimuli. This experiment resembled a typical examination of these mental functions with the single task demanding focused and the dual task conditions requiring divided attention. Both conditions activated a widespread, mainly right-sided network including dorso- and ventrolateral prefrontal structures, superior and inferior parietal cortex, and anterior cingulate gyrus. Under higher cognitive demands of divided attention, activity in these structures was enhanced and left-sided homologues were recruited. In a second experiment investigating another 17 subjects with almost the same paradigm, it was accounted for that in most dual task investigations of focused and divided attention the single tasks are easier to process than their combined presentation. Therefore, the task difficulty of focused attention tasks was increased. Almost the same activity pattern observed during division of attention was now found during focusing attention. Comparing both attentional states matched for task difficulty, differences were found in visual but not in prefrontal or parietal cortex areas. Our results suggest that focused and divided attention depend on largely overlapping neuronal substrates. Differences in activation patterns, especially in prefrontal and parietal areas, may result from unequal demands on executive control due to disparate processing requirements in typical tasks of focused and divided attention: Easier conditions begin with mainly right-sided activity within the attention network. As conditions become more difficult, left-lateralized homologue areas activate.

Neuronal operations associated with the top–down control process of shifting attention from one locus to another involve a network of cortical regions, and their influence is deemed fundamental to visual perception. However, the extent and nature of these operations within primary visual areas are unknown. In this paper, we used magnetoencephalography (MEG) in combination with magnetic resonance imaging (MRI) to determine whether, prior to the onset of a visual stimulus, neuronal activity within early visual cortex is affected by covert attentional shifts. Time/frequency analyses were used to identify the nature of this activity. Our results show that shifting attention towards an expected visual target results in a late-onset (600 ms postcue onset) depression of alpha activity which persists until the appearance of the target. Independent component analysis (ICA) and dipolar source modeling confirmed that the neuronal changes we observed originated from within the calcarine cortex. Our results further show that the amplitude changes in alpha activity were induced not evoked (i.e., not phase-locked to the cued attentional task). We argue that the decrease in alpha prior to the onset of the target may serve to prime the early visual cortex for incoming sensory information. We conclude that attentional shifts affect activity within the human calcarine cortex by altering the amplitude of spontaneous alpha rhythms and that subsequent modulation of visual input with attentional engagement follows as a consequence of these localized changes in oscillatory activity.

Attention effects on the processing of deviations in the duration and the frequency dimension of a long sound were investigated in three conditions: (1) when auditory stimuli were ignored, (2) when they were attended and frequency dimension was task-relevant, and (3) when they were attended and duration dimension was task-relevant. The mismatch negativity (MMN) of the event-related potential (ERP) to infrequent shortenings of a sound (600 ms vs. 1000 ms) and to infrequent frequency modulations at one of nine possible intervals within the sound (change from 440 Hz to 480 Hz and back to 440 Hz, e.g. in the 600–650 ms interval) was measured. Duration MMN was slightly enhanced when directing attention towards the frequency dimension but notably enhanced when attention was focused on duration. The early phase of frequency-modulated MMN was of equal amplitude in all three conditions, and the late phase was equally enlarged in both attend conditions. Interestingly, MMN to frequency-modulated deviants decreased the later the deviation occurred within the sound; there was no indication for an MMN being present in Ignore condition when frequency modulations occurred 400 ms after sound onset or later. Thus, with increasing temporal distance between the onset of a sound and the onset of a deviation within the sound (e.g. frequency modulation or sound offset), MMN for frequency modulations and duration shortenings decreases. This suggests that the initial part of a sound (∼300 ms) contributes more to the unitary sound representation underlying MMN than the later parts.

The effects of selective attention on the neural response to the violation of musical syntax were investigated in the present study. Musical chord progressions were played to nonmusicians while Event-Related Potentials (ERPs) were recorded. The five-chord progressions included 61% harmonically expected cadences (I–I⁶–IV–V–I), 26% harmonically unexpected cadences (I–I⁶–IV–V–N⁶), and 13% with one of the five chords having an intensity fadeout across its duration. During the attended condition, subjects responded by pressing a button upon detecting a fadeout in volume; during the unattended condition, subjects were given reading comprehension materials and instructed to ignore all auditory stimuli. In response to the harmonic deviant, an Early Anterior Negativity (EAN) was observed at 150–300 ms in both attention conditions, but it was much larger in amplitude in the attended condition. A second scalp-negative deflection was also identified at 380–600 ms following the harmonic deviants; this Late Negativity onset earlier during the attended condition. These results suggest strong effects of attention on the neural processing of harmonic syntax.

According to the model hypothesized by Näätänen and Michie (Biol Psychol 1979; 8: 81–136), the generation of the mismatch negativity (MMN) requires a mismatch detection, taking place in temporal areas, followed by the activation of frontal generators, underlying attention switching toward the deviant stimulus. We aimed at verifying whether the activation of temporal and frontal regions is dependent on the amount of attentional resources allocable toward the deviant stimulus. We recorded event-related potentials (ERPs) in nine healthy subjects while reading and during a demanding visual task (Multiple Features Target Cancellation, MFTC). Raw data were further evaluated by Brain Electrical Source Analysis (BESA). During the Reading condition, distraction toward the unattended auditory stimuli was reflected by the enhancement of the N1 response to frequent stimuli and by the elicitation of a P3a response to deviant ones. The MMN distribution was explained by bilateral temporal dipoles. During the MFTC condition, no P3a was detected, while source analysis showed the activation of a right frontal generator. Temporal dipoles showed no change between the two conditions: we thus conclude that the earlier mismatch detection is independent on the attentional load. By contrast, the activation of a right frontal subcomponent occurred only during the high-load task, independently on any actual attention shift reflected by the P3a component. We thus discuss the hypothesis whether the right frontal MMN generator, rather than subserving a simple attention switching toward the deviant stimulus, plays a role in modulating the auditory change detection system (“contrast enhancement” model).

Functional magnetic resonance imaging and a meta-analysis of prior neuroimaging studies were used to characterize cortical changes resulting from extensive practice and to evaluate a dual-processing account of the neural mechanisms underlying human learning. Three core predictions of the dual processing theory are evaluated: 1) that practice elicits generalized reductions in regional activity by reducing the load on the cognitive control mechanisms that scaffold early learning; 2) that these control mechanisms are domain-general; and 3) that no separate processing pathway emerges as skill develops. To evaluate these predictions, a meta-analysis of prior neuroimaging studies and a within-subjects fMRI experiment contrasting unpracticed to practiced performance in a paired-associate task were conducted. The principal effect of practice was found to be a reduction in the extent and magnitude of activity in a cortical network spanning bilateral dorsal prefrontal, left ventral prefrontal, medial frontal (anterior cingulate), left insular, bilateral parietal, and occipito-temporal (fusiform) areas. These activity reductions are shown to occur in common regions across prior neuroimaging studies and for both verbal and nonverbal paired-associate learning in the present fMRI experiment. The implicated network of brain regions is interpreted as a domain-general system engaged specifically to support novice, but not practiced, performance.