Cognitive Brain Research最新文献

This study examined hand preference in baboons in a sample of 94 subjects for a unimanual task and in a sample of 104 subjects for a bimanual task. For the unimanual task, handedness was assessed by observing simple reaching for grains. For the bimanual task, tubes lined with peanut butter inside were presented to the baboons. The hand and the finger used to remove peanut butter were recorded. Population-level right-handedness was found for the bimanual but not the unimanual task. In addition, test–retest correlations showed consistency in hand use across time for the coordinated bimanual task but not the simple reaching task. No significant effects of age and sex on the direction and strength of hand preferences were found for either task. These are the first evidences of population-level handedness in baboons and the results are discussed in the context of evolutionary theories of cerebral dominance.

This study sought to evaluate impaired response tendencies and modulation of automatic processes in Parkinson's disease (PD), utilising a saccadic Simon task with stimulus–response (S–R) compatibility determined on the basis of cue shape. The appearance of either a circle or a square in one of two boxes presented peripherally required the generation of a leftward or rightward horizontal saccade, respectively. These goal-directed responses were considered behaviourally relevant to an examination of visuospatial performance. Although response times are typically faster when stimulus and response are spatially compatible than when they are not, sequence-dependent modulation of this effect results in large differences between S–R compatible and S–R incompatible trials when stimulus and response are spatially compatible in the preceding trial, and reduced or absent differences when stimulus and response are spatially incompatible in the preceding trial. Unlike control subjects, PD patients demonstrated significantly shorter saccadic latencies overall, compared to a baseline condition involving endogenously-driven saccades. Patients also responded erroneously to cue stimuli with greater frequency. Analyses of both saccadic latency and errors to cue demonstrated a Simon effect (relatively faster response for S–R compatible trials), irrespective of the preceding trial. This suggests impaired modulation of the Simon effect in PD, consistent with predictions of inhibitory dysfunction, or impaired episodic memory. These results demonstrate the pivotal role of the basal ganglia in the regulation of context-dependent neural activity.

One of the major problems in affective neuroscience of healthy subjects as well as of patients with emotional dysfunctions is to disentangle emotional core functions and non-emotional processes. Emotional valence is considered an emotional key process. The present study employed a parametric functional magnetic resonance imaging (fMRI) study to address this question. Thirteen healthy volunteers were scanned during emotional stimulus processing (International Affective Picture System). The presented pictures covered the entire range of emotional valences. The fMRI data were consecutively subjected to a preliminary categorical (valence-independent) and a detailed parametric analysis, the latter using individual valence ratings as regressor. The parametric analysis revealed a linear valence-dependent modulation of the BOLD signal in the orbito- and dorsomedial prefrontal cortex (OMPFC, DMPFC), medial parietal cortex (MPC), and insula. In addition, we observed that emotional valence exerts its effects predominantly via modulation of signal decreases. We conclude that the psychological concept of emotional valence may be related to neural processing in cortical midline regions.

When judging the relative magnitude of the left and right sides of a stimulus, normal participants overestimate the leftward features (pseudoneglect). Although pseudoneglect and clinical neglect operate in opposite directions, the two phenomena may have a common cognitive and neural basis. For neglect, two strategies may be employed when inspecting horizontally aligned stimuli: (1) A global strategy where the stimuli are treated as a gestalt and asymmetries are detected or, (2) a comparison strategy where the qualities on the left and right sides of the stimuli are explicitly compared. To investigate the effect of these strategies on pseudoneglect, normal dextrals (n = 25 and 17) made two-alternative, forced-choice luminance discriminations between two mirror-reversed luminance gradients (greyscales). In an unseparated form, the stimuli are amenable to a global strategy. A comparison strategy was imposed by separating the stimuli into halves (Experiment 1) or quarters (Experiment 2). Despite the fact that the stimuli were equiluminant, participants predominantly chose the stimulus that was dark on the left as being darker overall in the unseparated condition. Response times were also faster for leftward responses. When the stimuli were separated into halves or quarters, the leftward bias was reduced, but not eliminated. The results demonstrate that both strategies contribute to pseudoneglect—though the global strategy may produce stronger pseudoneglect.

We studied eye movements during mental extrapolation of motion. Subjects tracked with the eyes a target oscillating sinusoidally by ± 5° on the horizontal plane at frequencies between 0.15 and 0.5 Hz. After 4 cycles the target disappeared and subjects had to mentally extrapolate its motion in imagery for 5 further cycles. Subjects were invited to relax. We recorded eye movements with infrared oculography and the lid aperture with a webcam. Typically, in the imagery phase, sequences of saccades “reproduced” the macroscopic characteristics of the to-be-imagined motion. However, slow eye movements substituting the sequence of saccades emerged repeatedly in the course of the experiment, to the extent that sometimes it was almost impossible to distinguish the pattern of eye movements during tracking from that during imagery. These smooth pursuit-like eye movements lasted up to 17 s, although they were more commonly intermingled with saccades. It turned out that this phenomenon occurred mostly, although not exclusively, when the lids were partially lowered suggesting an association with drowsiness. The average gain of smooth pursuit-like eye movements in imagery passed from 0.09 when the lids were open, to 0.27 when they were partially lowered. A control experiment excluded that the lowering of the lids per se had played any important role. This finding has implications for both the physiology of the oculomotor system and for the debate on the relation between imagery and perception.

Event-related potentials (ERPs) were acquired during two experiments in order to determine boundary conditions for when recollection of colour information can be controlled strategically. In initial encoding phases, participants saw an equal number of words presented in red or green. In subsequent retrieval phases, all words were shown in white. Participants were asked to endorse old words that had been shown at encoding in one colour (targets), and to reject new test words as well as old words shown in the alternate colour (non-targets). Study and test lists were longer in Experiment 1, and as a result, the accuracy of memory judgments was superior in Experiment 2. The left-parietal ERP old/new effect—the electrophysiological signature of recollection—was reliable for targets in both experiments, and reliable for non-targets in Experiment 1 only. These findings are consistent with the view that participants were able to restrict recollection to targets in Experiment 2, while recollecting information about targets as well as non-targets in Experiment 1. The fact that this selective strategy was implemented in Experiment 2 despite the close correspondence between the kinds of information associated with targets and non-targets indicates that participants were able to exert considerable control over the conditions under which recollection of task-relevant information occurred.

Large individual differences are commonly observed during the early stages of category learning in both functional MRI (fMRI) activation maps and behavioral data. The current investigation characterizes this variability by correlating the volume of activation with behavioral performance. Healthy subjects were trained to classify patterns of random dots into categories. Training was carried out using a 4-choice categorization task with feedback. Functional MRI was performed prior to any training and then following each of 3 training sessions. The fMRI sessions involved the presentation of 3 separate paradigms which required the skill imparted by the training to determine whether two patterns of dots belonged to the same category. Contrasts between the 3 paradigms allowed the examination of the effects of training and of familiarity with the task. For fMRI performed with those materials used during training, increases in the volume of activation were observed initially. As behavioral performance continued to improve, reductions in activation were observed across regions involved in visuospatial processing and spatial attention. These reductions in activation were observed only for those materials used in training and only after high levels of performance were achieved. The magnitude of these reductions in activation correlated with each individual's own rate of learning. The present data support the observation that at least two stages of cortical activation underlie the use of newly learned categories. The first, recruitment of nearby tissue, is observed as initial increases in the volumes of activation. These initial stages of recruitment are followed by specialization across the same network which is observed as a reduction in activation with continued improvements in behavioral performance.

Neural processes underlying pitch perception at the level of the cerebral cortex are influenced by language experience. We investigated whether early, pre-attentive stages of pitch processing at the level of the human brainstem may also be influenced by language experience. The human frequency following response (FFR), reflecting sustained phase-locked activity in a population of neural elements, was used to measure activity within the rostral brainstem. FFRs elicited by four Mandarin tones were recorded from native speakers of Mandarin Chinese and English. Pitch strength (reflecting robustness of neural phase-locking at the pitch periods) and accuracy of pitch tracking were extracted from the FFRs using autocorrelation algorithms. These measures revealed that the Chinese group exhibits stronger pitch representation and smoother pitch tracking than the English group. Consistent with the pitch data, FFR spectral data showed that the Chinese group exhibits stronger representation of the second harmonic relative to the English group across all four tones. These results cannot be explained by a temporal pitch encoding scheme which simply extracts the dominant interspike interval. Rather, these results support the possibility of neural plasticity at the brainstem level that is induced by language experience that may be enhancing or priming linguistically relevant features of the speech input.

In order to clarify the respective contribution of the right and left posterior parietal cortex (PPC) to number comparison, transcranial magnetic stimulation (TMS) was used to disrupt PPC processing in subjects instructed to determine whether a digit was smaller or larger than 5. Single pulse TMS was applied over the PPC, either unilaterally or bilaterally, 150, 200, or 250 ms after digit presentation. Sham TMS was used as a control condition to take into account the unspecific effects of TMS on reaction time (RT). The main finding of the present study is a significant increase in RTs when comparing digits close to 5 following a disruption either of the left PPC alone or of both PPC simultaneously. The comparison of digits far from 5 was unaltered by disrupting only one PPC but RTs were found increased after bilateral PPC stimulation. These disruptive effects were observed irrespective of the TMS delay. We concluded that coding precise numerical values requires the integrity of the left PPC, as suggested by the deficit in discriminating close digits consequent to its disruption. In contrast, approximate comparisons can be processed either by the left or right PPC, since simultaneous bilateral TMS was needed to alter the comparison of digits far from 5.