Recruitment of lateral rostral prefrontal cortex in spontaneous and task-related thoughts

Behavioural and neuroimaging studies suggest that spontaneous and task-related thought processes share common cognitive mechanisms and neural bases. Lateral rostral prefrontal cortex (RPFC) is a brain region that has been implicated both in spontaneous thought and in high-level cognitive control processes, such as goal/subgoal integration and the manipulation of self-generated thoughts. We therefore propose that the recruitment of lateral RPFC may follow a U-shaped function of cognitive demand: relatively high in low-demand situations conducive to the emergence of spontaneous thought, and in high-demand situations depending on processes supported by this brain region. We used functional magnetic resonance imaging to investigate brain activity while healthy participants performed two tasks, each with three levels of cognitive demands, in a block design. The frequency of task-unrelated thoughts, measured by questionnaire, was highest in the low cognitive demand condition. Low and high cognitive demand conditions were each compared to the intermediate level. Lateral RPFC and superior parietal cortex were recruited in both comparisons, with additional activations specific to each contrast. These results suggest that RPFC is involved both when (a) task demands are low, and the mind wanders, and (b) the task requires goal/subgoal integration and manipulation of self-generated thoughts.     

Functional cerebral changes in multiple sclerosis patients during an autobiographical memory test

Our aim was to investigate the functional underpinnings of autobiographical memory (AM) impairment in multiple sclerosis (MS) patients. To that end, 18 patients and 18 controls underwent the autobiographical interview (AI). Subsequently, the 36 participants underwent a functional magnetic resonance imaging (fMRI) session designed to assess the construction and elaboration of AMs. A categorical control task was also presented. Patients were trained in the fMRI procedure to optimise the procedural aspects accompanying the task itself. Although the patients obtained significantly poorer AI scores (p < .001), their performance on the easier AM fMRI task was efficiently carried out, allowing relevant comparisons with healthy controls. Relatively to healthy controls, the patients showed increased and bilateral cerebral activations (p < .005) during the construction and elaboration phases. The prefrontal, temporal and posterior cerebral region activations were located within the core network sustaining AM, with the bilateral prefrontal region being centrally involved. The parametric neural responses to the difficulty of access and amount of details of memories were also significantly different for the two groups, with the right hippocampal region showing a particularly increased recruitment (p < .005). The findings suggested the presence of functional cerebral changes during AM performance and supported the presence of AM retrieval deficit in MS patients.     

Neuronal correlates of decisions to speak and act: Spontaneous emergence and dynamic topographies in a computational model of frontal and temporal areas

The neural mechanisms underlying the spontaneous, stimulus-independent emergence of intentions and decisions to act are poorly understood. Using a neurobiologically realistic model of frontal and temporal areas of the brain, we simulated the learning of perception–action circuits for speech and hand-related actions and subsequently observed their spontaneous behaviour. Noise-driven accumulation of reverberant activity in these circuits leads to their spontaneous ignition and partial-to-full activation, which we interpret, respectively, as model correlates of action intention emergence and action decision-and-execution. Importantly, activity emerged first in higher-association prefrontal and temporal cortices, subsequently spreading to secondary and finally primary sensorimotor model-areas, hence reproducing the dynamics of cortical correlates of voluntary action revealed by readiness-potential and verb-generation experiments. This model for the first time explains the cortical origins and topography of endogenous action decisions, and the natural emergence of functional specialisation in the cortex, as mechanistic consequences of neurobiological principles, anatomical structure and sensorimotor experience.     

Spatial correspondence between onsets and offsets of stimuli and responses

The Simon effect denotes faster responses when the task-irrelevant stimulus position corresponds to response position than when it does not. A common explanation is that a spatial stimulus code is formed automatically and activates a spatially corresponding response code. Previous research on stimulus–response (S–R) compatibility has focused on the ability to initiate movements to stimulus onsets. The present study investigates spatial-compatibility effects (i.e., the Simon effect) in the ability to initiate and to terminate actions both to stimulus onsets and to stimulus offsets. There were four major results. Firstly, offset stimuli produced normal Simon effects suggesting that stimulus offsets can automatically produce spatial codes. Secondly, onset stimuli produced larger Simon effects than offset stimuli, which is consistent with the attention-shift account of spatial coding. Thirdly, Simon effects were also observed in action termination. Fourthly, Simon effects in action initiation and in action termination were of similar size.     

Functions of parahippocampal place area and retrosplenial cortex in real-world scene analysis: An fMRI study

We used functional MRI to investigate several hypotheses concerning the functions of posterior parahippocampal cortex and retrosplenial cortex, two regions that preferentially activate to images of real-world scenes compared to images of other meaningful visual stimuli such as objects and faces. We compared activation resulting from photographs of rooms, city streets, cityscapes, and landscapes against activation to a control condition of objects. Activation in posterior parahippocampal cortex, including parahippocampal place area, was greater for all scene types than objects, and greater for scenes that clearly convey information about local three-dimensional (3-D) structure (city streets and rooms) than scenes that do not (cityscapes and landscapes). Similar differences were observed in retrosplenial cortex, though activation was also greater for city streets than rooms. These results suggest that activation in both cortical areas is primarily related to analysis or representation of local 3-D space. The results are not consistent with hypotheses that these areas reflect panoramic spatial volume, an artificial versus natural category distinction, an indoor versus outdoor distinction, or the number of explicit objects depicted in a scene image.     

A Preliminary Investigation of the Assessment and Treatment of Tantrums With Two Post-Institutionalized Romanian Adoptees

A functional analysis of tantrums was carried out with 2 children who were adopted from state-run Romanian orphanages. Tantrums included such behaviours as screaming, property destruction, self-injury and aggression. The functional analysis was conducted in an outpatient treatment unit and consisted of exposing the child and mother to a number of specific social contexts that were designed to identify social consequences maintaining tantrums. These social contexts were alternated rapidly in a multi-element design fashion during the outpatient assessment to demonstrate experimental control. Results indicated that tantrums were maintained by attention from the mother when the mother's attention was diverted away from the child (i.e. when the mother was interacting with another person). A treatment plan, which consisted of the mother delivering frequent but brief attention statements to the child during diverted attention contexts eliminated tantrums during the assessment. Follow-up evaluations for up to 6 months indicated that parents used the treatment plan and that tantrums were no longer a difficulty with these children.     

Perceptual visual grouping under inattention: electrophysiological functional imaging

Two types of perceptual visual grouping, differing in complexity of shape formation, were examined under inattention. Fourteen participants performed a similarity judgment task concerning two successive briefly presented central targets surrounded by task-irrelevant simple and complex grouping patterns. Event-related potentials (ERPs) were recorded from 22 scalp electrodes and source current density estimations were conducted for the net response to the task-irrelevant background patterns, using low-resolution electromagnetic tomography (LORETA). Although participants’ subjective reports indicated that neither type of organization induced awareness, electrophysiological results showed they both evoked significant activation in occipital, parieto-temporal and frontal brain areas. Behavioral results demonstrated that only grouping of the simple pattern arose under inattention. In contrast to the complex pattern, the processing of the simple pattern was associated with an initially longer latency and higher activation beginning at 130 ms. These results support the distinction of grouping patterns differing in complexity of shape formation.     

Neuroanatomical correlates of processing in visual and visuospatial working memory

Working memory is traditionally seen as being organised in a modular way with a central executive orchestrating at least two slave systems (phonological loop and visuospatial sketch pad). Neuroanatomical correlates of the visual and visuospatial subsystems and the central executive are discussed in this article. A series of experiments are presented yielding evidence for a differentiation into active and passive processing in working memory as well as their neuroanatomical correlates in the prefrontal cortex. Data, yielding evidence for an interaction and separation of visual and visuospatial working memory are presented and discussed. Further results are presented which suggest a convergence of these two systems with increasing working memory demands. The discussed findings will give new insight in the organisation of visual and visuospatial working memory on the anatomical level.     

Bimanual tapping of a syncopated rhythm reveals hemispheric preferences for relative movement frequencies

In bimanual multifrequency tapping, right-handers commonly use the right hand to tap the relatively higher rate and the left hand to tap the relatively lower rate. This could be due to hemispheric specializations for the processing of relative frequencies. An extension of the double-filtering-by-frequency theory to motor control proposes a left hemispheric specialization for the control of relatively high and a right hemispheric specialization for the control of relatively low tapping rates. We investigated timing variability and rhythmic accentuation in right handers tapping mono- and multifrequent bimanual rhythms to test the predictions of the double-filtering-by-frequency theory. Yet, hemispheric specializations for the processing of relative tapping rates could be masked by a left hemispheric dominance for the control of known sequences. Tapping was thus either performed in an overlearned quadruple meter (tap of the slow rhythm on the first auditory beat) or in a syncopated quadruple meter (tap of the slow rhythm on the fourth auditory beat). Independent of syncopation, the right hand outperformed the left hand in timing accuracy for fast tapping. A left hand timing benefit for slow tapping rates as predicted by the double-filtering-by-frequency theory was only found in the syncopated tapping group. This suggests a right hemisphere preference for the control of slow tapping rates when rhythms are not overlearned. Error rates indicate that overlearned rhythms represent hierarchically structured meters that are controlled by a single timer that could potentially reside in the left hemisphere.     

自闭症谱系障碍者异常的大脑功能连接

自闭症谱系障碍(Autism spectrum disorders, ASD)是一种常见的神经发育障碍, ASD在社交、语言、行为等方面的障碍与其异常的大脑功能连接存在密切关系。与正常发育者相比, ASD大脑既表现出远距离功能连接不足, 也表现出局部功能连接过度增强。ASD这种异常的脑功能连接受到结构异常、扫描状态、个体发展、分析方法等多种因素的影响。未来的ASD脑机制研究中, 要综合分析脑功能与结构, 关注年龄发展变化, 并将任务状态、被试取样、数据分析标准等因素纳入考察。