Electroencephalographic oscillations at 10Hz (alpha and mu rhythms) are the most prominent rhythms observed in awake, relaxed (eye-closed) subjects. These oscillations may be considered as a marker of cortical inactivity or an index of the active inhibition of the sensory information. Different cortical sources may participate in the 10-Hz oscillation and appear to be modulated by the sensory context and functional demands. In microgravity, the marked reduction in multimodal graviceptive inputs to cortical networks participating in the representation of space could be expected to affect the 10-Hz activity. The effect of microgravity on this basic oscillation has heretofore not been studied quantitatively. Because the alpha rhythm has a functional role in the regulation of network properties of the visual areas, we hypothesised that the absence of gravity would affect its strength. Here, we report the results of an experiment conducted over the course of 3 space flights, in which we quantified the power of the 10-Hz activity in relation to the arrest reaction (i.e., in 2 distinct physiological states: eyes open and eyes closed). We observed that the power of the spontaneous 10-Hz oscillation recorded in the eyes-closed state in the parieto-occipital (alpha rhythm) and sensorimotor areas (mu rhythm) increased in the absence of gravity. The suppression coefficient during the arrest reaction and the related spectral perturbations produced by eye-opening/closure state transition also increased in on orbit. These results are discussed in terms of current theories on the source and the importance of the alpha rhythm for cognitive function.
The present study tracked the naming-related brain activity by positron emission tomography (PET) when successfully learned unfamiliar objects were named. Ten Finnish-speaking subjects participated in the study. Prior to the PET scan, each subject underwent a 4-day long training period in which 40 names of rare unfamiliar objects were taught. The stimulus categories were as follows: unfamiliar but real objects for which both the name and the definition were given during training, only the name was given, no information was given. In addition, familiar objects and visual noise patterns were used. The unfamiliar items mainly represented ancient domestic tools unknown to modern-day people. As semantic support did not affect the PET results, all trained items were pooled together. The trained objects vs. familiar objects contrast revealed rCBF increases in the left inferior frontal cortex (Broca's area), the left anterior temporal area, and the cerebellum. Likewise, the trained objects vs. unfamiliar objects (for which no information was given) contrast revealed more extensive left frontal (roughly Broca's area) and cerebellar rCBF increases, while anterior temporal activation was bilateral. Familiar objects, contrasted with both visual noise patterns and a rest condition, elicited activation increases in expected areas, i.e., bilateral occipital regions and the fusiform gyrus. Our results indicate that the naming of newly learned objects recruits more extensive brain areas than the naming of familiar items, namely a network that includes left-dominant frontotemporal areas and cerebellum. Its activity is tentatively related to enhanced lexical–semantic and lexical–phonological retrieval, as well as associative memory processes.
In the present study, we examined stimulus-driven neuromagnetic activity in a delayed Pavlovian aversive conditioning paradigm using steady state visual evoked fields (SSVEF). Subjects showing an accelerative heart rate (HR) component to the CS+ during learning trials exhibited an increased activation in sensory and parietal cortex due to CS+ depiction in the extinction block. This was accompanied by a selective orientation response (OR) to the CS+ during extinction as indexed by HR deceleration. However, they did not show any differential cortical activation patterns during acquisition. In contrast, subjects not showing an accelerative HR component but rather unspecific HR changes during learning were characterized by greater activity in left orbito-frontal brain regions in the acquisition block but did not show differential SSVEF patterns during extinction. The results suggest that participants expressing different HR responses also differ in their stimulus-driven neuromagnetic response pattern to an aversively conditioned stimulus.
Williams syndrome (WS) is a neurodevelopmental disorder of genetic origin that has been used as a model to understand visual cognition. We have investigated early deficits in the afferent magnocellular pathway and their relation to abnormal visual dorsal processing in WS. A spatiotemporal contrast sensitivity task that is known to selectively activate that pathway was used in six WS subjects. Additionally, we have compared visual performance in 2D and 3D motion integration tasks. A novel 3D motion coherence task (using spheres with unpredictable axis of rotation) was used in order to investigate possible impairment of occipitoparietal areas that are known to be involved in 3D structure from motion (SFM) perception. We have found a significant involvement of low-level magnocellular maps in WS as assessed by the contrast sensitivity task. On the contrary, no significant differences were observed between WS and the control groups in the 2D motion integration tasks. However, all WS subjects were significantly impaired in the 3D SFM task. Our findings suggest that magnocellular damage may occur in addition to dorsal stream deficits in these patients. They are also consistent with recently described genetic and neuroanatomic abnormalities in retinotopic visual areas. Finally, selective SFM coherence deficits support the proposal that there is a specific pathway in the dorsal stream that is involved in motion processing of 3D surfaces, which seems to be impaired in this disorder.
If stimulation occasionally contains distracting information, behavioral responses to task-relevant aspects of the stimulation are prolonged and more error prone. Additionally, event-related potentials (ERPs) acquired in an auditory distraction paradigm show that the distracting information elicits the components mismatch negativity (MMN), P3a and reorienting negativity (RON). Here, we assess to what extent sequential dependencies in the stimulation influence such indicators of distraction. Data of four experiments were reanalyzed for response repetition and response change trials separately. Behavioral performance on Deviants suggests markedly smaller distraction effects in change compared to repetition trials. However, the presence of MMN–P3a–RON in both response repetition and response change trials shows that sequential features in stimulation do not dissolve distraction, but might substantially contribute to the (behavioral) effects measured in distraction paradigms and should be controlled for.
Although the age of acquisition of a language has an effect when learning a second language, the similarity between languages may also have a crucial role. The aim of the present study is to understand the influence of this latter factor in the acquisition of morphosyntactic information. With this purpose, two groups of highly proficient early Catalan–Spanish bilinguals were presented with a repetition-priming paradigm with regular and irregular verbs of Spanish. Catalan and Spanish have a similar suffix (-o) for regular verbs and completely different alternations for irregular verbs. Two types of irregular verbs were studied (semi-regular verbs with a systematic diphthong alternation, sentir–siento, and verbs with idiosyncratic changes, venir–vengo). Regular verbs showed the same centro-parietal N400 priming effect in the second-language speakers (L2) as in primary-language (L1) speakers. However, differences between groups, in the ERP pattern and the topography of the N400 effect, were observed for irregular morphology. In L1 speakers, the N400 effect was attenuated only for semi-regular verbs. In contrast, L2 speakers showed a reduced N400 priming effect in both irregular contrasts. This pattern of results suggests that the similarity between languages may help for similar structures but may interfere for dissimilar structures, at least when the two languages have very similar morphological systems.
A considerable recent literature argues that the same representations, encoded by inferior prefrontal and parietal cells known as “mirror neurons”, may be activated in both production and recognition of object-related actions. Here, we test several predictions derived from the contemporary literature on the parity between production and recognition and the putative emergence of the mirror neuron system from a system coding hand–object interactions. Forty-four patients with left-hemisphere stroke, 21 of whom exhibited ideomotor apraxia, performed a number of pantomime imitation and recognition tasks, and performance was scored with respect to hand posture, arm posture, amplitude, and timing. Consistent with predictions, there were strong relationships between object-related pantomime imitation and object-related pantomime recognition, and between imitation and recognition of the hand posture component of object-related actions. Skilled object-related gesture representations are likely to be closely tied to evolutionarily more primitive systems controlling object grasping, to emerge from a mapping between object and action information coded by ventral and dorsal streams, and to be lateralized to the left hemisphere in humans.
Behavioral studies have suggested that bistable figure perception is mediated by spatial attention. We tested this hypothesis using event-related functional MRI. During central fixation, two tilted squares containing coherently moving dots were presented in the left and right hemifields. In the attention condition, participants were occasionally cued to shift attention between the squares. In the perception condition, corresponding corners of the squares were connected by horizontal lines producing a perceptually bistable Necker cube figure. Observers reported which of the two faces appeared 'forward' in depth; cues elicited voluntary perceptual reversals. Attending to either square during the attention condition or perceiving either square as forward during the perception condition yielded increased activity in contralateral visual areas. Furthermore, voluntary shifts of attention and voluntary shifts in perceptual configuration were associated with common activity in the posterior parietal cortex, part of the frontoparietal attentional control network. These results support the hypothesis that voluntary shifts in perceptual bistability are mediated by spatial attention.
Horizontal line bisection is a ubiquitous task in the investigation of visual neglect. Patients with left neglect typically make rightward errors that increase with line length and for lines at more leftward positions. For short lines, or for lines presented in right space, these errors may 'cross over' to become leftward. We have taken a new approach to these phenomena by employing a different set of dependent and independent variables for their description. Rather than recording bisection error, we record the lateral position of the response within the workspace. We have studied how this varies when the locations of the left and right endpoints are manipulated independently. Across 30 patients with left neglect, we have observed a characteristic asymmetry between the 'weightings' accorded to the two endpoints, such that responses are less affected by changes in the location of the left endpoint than by changes in the location of the right. We show that a simple endpoint weightings analysis accounts readily for the effects of line length and spatial position, including cross-over effects, and leads to an index of neglect that is more sensitive than the standard measure. We argue that this novel approach is more parsimonious than the standard model and yields fresh insights into the nature of neglect impairment.
To better understand the nature and time course for learning-induced cortical reorganization, we examined frequency-specific changes in auditory cortex as cats gradually improved at a difficult sound frequency discrimination task. Three adult cats were trained to discriminate between a tone pip at a fixed target frequency (S-) and a higher deviant frequency (S+). An adaptive training schedule led to an efficient estimate of the frequency discrimination threshold (FDT), which was used to track daily performance. Each cat was also implanted with an array of microwires in auditory cortex. Tone pips with different frequency and amplitude were used to map receptive fields. Onset responses were correlated with training time and the cat's ability to discriminate frequencies.Although lifetime of the neural implants varied among cats, each provided sufficient neural recording to relate at least 3 weeks of learning to response changes in the cortex. An improved FDT was associated with a differential decrease in response strength between the S-frequency and S+ frequencies. Response to the training frequencies gradually located in a local minimum compared to adjacent frequencies (p < 0.001, Cohen's d = 0.50). Cortical changes were consistent with a theory of bimodal generalization that enhances stimulus classification by reducing similarity between reinforced and nonreinforced stimuli. Such a strategy may be especially appropriate during an early stage of learning to discriminate similar sounds and differ from later strategies required for fine discrimination. (c) 2004 Elsevier B.V. All rights reserved.
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.
To better understand whether voluntary attention affects how the brain processes novel events, variants of the auditory novelty oddball paradigm were presented to two different groups of human volunteers. One group of subjects (n=16) silently counted rarely presented 'infrequent' tones (p=0.10), interspersed with 'novel' task-irrelevant unique environmental sounds (p=0.10) and frequently presented 'standard' tones (p=0.80). A second group of subjects (n=17) silently counted the 'novel' environmental sounds, the 'infrequent' tones now serving as the task-irrelevant deviant events. Analysis of event-related potentials (ERPs) recorded from 63 scalp channels suggested a spatiotemporal overlap of fronto-central novelty P3 and centro-parietal P3 (P3b) ERP features in both groups. Application of independent component analysis (ICA) to concatenated single trials revealed two independent component clusters that accounted for portions of the novelty P3 and P3b response features, respectively. The P3b-related ICA cluster contributed to the novelty P3 amplitude response to novel environmental sounds. In contrast to the scalp ERPs, the amplitude of the novelty P3 related cluster was not affected by voluntary attention, that is, by the target/nontarget distinction. This result demonstrates the usefulness of ICA for disentangling spatiotemporally overlapping ERP processes and provides evidence that task irrelevance is not a necessary feature of novelty processing.
Using positron emission tomography (PET), we investigated the organisation of spatial versus object-based visual working memory in 11 normal human subjects. The paradigm involved a conditional colour-response association task embedded within two visual working memory tasks. The subject had to remember a position (spatial) or shape (object-based) and then use this to recover the colour of the matching element for the conditional association. Activation of the nucleus accumbens and the anterior cingulate cortex was observed during the conditional associative task, indicating a possible role of these limbic structures in associative memory. When the 2 memory tasks were contrasted, we observed activation of 2 distinct cortical networks: (1) The spatial task activated a dorsal stream network distributed in the right hemisphere in the parieto-occipital cortex and the dorsal prefrontal cortex, and (2) The non spatial task activated a ventral stream network distributed in the left hemisphere in the temporo- occipital cortex, the ventral prefrontal cortex and the striatum. These results support the existence of a domain-specific dissociation with dorsal and ventral cortical systems involved respectively in spatial and non spatial working memory functions.
The functional organization of the human auditory cortex is still not well understood with respect to speech perception and language lateralization. Especially, there is comparatively little data available in the brain imaging literature focusing on the timing of phonetic processing. We recorded auditory-evoked potentials (AEP) from 27 scalp and additional EOG channels in 12 healthy volunteers performing a free report dichotic listening task with simple speech sounds (CV syllables: [ba], [da], [ga], [pa], [ta], [ka]). ERP analysis employed independent components analysis (ICA) wavelet denoising for artifact reduction and improvement of the SNR. The main finding was a 15-ms shorter average latency of the N1-AEP recorded from the scalp approximately overlying the left supratemporal cortical plane compared to the N1-AEP over the homologous right side. Corresponding N1 amplitudes did not differ between these sites. The individual AEP latency differences significantly correlated with the ear advantage as an index of speech/language lateralization. The behaviorally relevant difference in N1 latency between the hemispheres indicates that an important key to understanding speech perception is to consider the functional implications of neuronal event timing.
Decision-making is an important aspect of daily life. Moreover, dysfunctions of decision-making play a critical role in a number of neuropsychiatric disorders. Several important research groups have contributed a diverse set of approaches to study decision-making and its underlying neurobiology. Insights from these studies may provide important directions for future research in this area.
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.
In this event-related fMRI study, 12 right-handed volunteers heard human laughter, sentential speech, and nonvocal sounds in which global temporal and harmonic information were varied whilst they were performing a simple auditory target detection. This study aimed to delineate distinct peri-auditory regions which preferentially respond to laughter, speech, and nonvocal sounds. Results show that all three types of stimuli evoked blood–oxygen-level-dependent responses along the left and right peri-sylvian cortex. However, we observed differences in regional strength and lateralization in that (i) hearing human laughter preferentially involves auditory and somatosensory fields primarily in the right hemisphere, (ii) hearing spoken sentences activates left anterior and posterior lateral temporal regions, (iii) hearing nonvocal sounds recruits bilateral areas in the medial portion of Heschl's gyrus and at the medial wall of the posterior Sylvian Fissure (planum parietale and parietal operculum). Generally, the data imply a differential regional sensitivity of peri-sylvian areas to different auditory stimuli with the left hemisphere responding more strongly to speech and with the right hemisphere being more amenable to nonspeech stimuli. Interestingly, passive perception of human laughter activates brain regions which control motor (larynx) functions. This observation may speak to the issue of a dense intertwining of expressive and receptive mechanisms in the auditory domain. Furthermore, the present study provides evidence for a functional role of inferior parietal areas in auditory processing. Finally, a post hoc conjunction analysis meant to reveal the neural substrates of human vocal timbre demonstrates a particular preference of left and right lateral parts of the superior temporal lobes for stimuli which are made up of human voices relative to nonvocal sounds.
In an event-related potential (ERP) study, brain correlates of temporal processing in the range of milliseconds were investigated by means of a dissociation paradigm. For this purpose, ten male and ten female subjects performed temporal and pitch generalization tasks with uni- and bidimensional stimulus variation. With difficulty held constant for both tasks, a larger frontally distributed negative slow wave was observed for pitch generalization relative to temporal generalization. This ERP pattern was consistent across uni- and bidimensional tasks of the present study but in direct contrast to prior ERP studies on temporal processing. Furthermore, for both uni- and bidimensional temporal tasks, within-task ERP analyses yielded amplitude modulation of centro-parietal P3b and fronto-central P500 as brain correlates of actively processed stimulus duration. Findings were consistent with a two-process model of temporal information processing based on a real-time comparison of the presented stimulus duration against an internal representation of the standard duration.
When participants judge the parity of visually presented digits, left-hand responses are faster for numerically small numbers, whereas right-hand responses are faster for large numbers [SNARC effect; S. Dehaene, S. Bossini, P. Giraux, The mental representation of parity and number magnitude. J. Exp. Psychol. Gen., 122, (1993) 371–396]. The present study aimed to find more direct evidence for the functional locus of this effect by recording brain waves while participants performed speeded parity judgments giving manual responses. Our results show clear and robust SNARC effects in the response-locked event-related potentials (ERPs) compared to the stimulus-locked ERPs, confirming that the SNARC effect arises during response-related rather than stimulus-related processing stages. Further analyses of lateralized readiness potentials strongly suggest that the SNARC effect begins to emerge in a response-related stage prior to response preparation and execution, more specifically, in a response selection stage.
In the field of physiological study of human intelligence, strong evidence of a more efficient operation (i.e., less activation) of the brain in brighter individuals (the neural efficiency hypothesis) can be found. Most studies in this field have used single, homogeneous tasks and have not examined sex differences. In analyzing the extent of Event-related Desynchronization (ERD) in the EEG during the performance of a verbal and a visuo-spatial task, we recently found that males and females display neural efficiency primarily in the domain where they usually perform better (i.e., verbal in females and spatial in males; cf. A.C. Neubauer, A. Fink, D.G. Schrausser, Intelligence and neural efficiency: the influence of task content and sex on brain-IQ relationship. Intelligence, 30 (2002) 515-536). However, this interpretation was complicated by differences in the complexity of the two tasks. By using a verbal (semantic) and a spatial (rotation) task of comparable complexity in this research, we sought to replicate and extend our earlier findings by additionally considering the individual differences in intelligence structure and the topographical distribution over the cortex. Findings were similar to the previous study: Females (n = 35) display neural efficiency (i.e., less brain activation in brighter individuals) primarily during the verbal task, males (n = 31) in the spatial task. However, the strength of this brain activation-IQ relationship varies with the intelligence factor: In males, the highest correlations were observed for spatial IQ, in females for verbal IQ. Furthermore, the sexes displayed topographical differences of neural efficiency patterns.
