Focusing Narrowly or Broadly Attention When Judging Categorical and Coordinate Spatial Relations: A MEG Study

We measured activity in the dorsal system of the human cortex with magnetoencephalography (MEG) during a matching-to-sample plus cueing paradigm, where participants judged the occurrence of changes in either categorical or coordinate spatial relations (e.g., exchanges of left versus right positions or changes in the relative distances) between images of pairs of animals. The attention window was primed in each trial to be either small or large by using cues that immediately preceded the matching image. In this manner, we could assess the modulatory effects of the scope of attention on the activity of the dorsal system of the human cortex during spatial relations processing. The MEG measurements revealed that large spatial cues yielded greater activations and longer peak latencies in the right inferior parietal lobe for coordinate trials, whereas small cues yielded greater activations and longer peak latencies in the left inferior parietal lobe for categorical trials. The activity in the superior parietal lobe, middle frontal gyrus, and visual cortex, was also modulated by the size of the spatial cues and by the type of spatial relation change. The present results support the theory that the lateralization of each kind of spatial processing hinges on differences in the sizes of regions of space attended to by the two hemispheres. In addition, the present findings are inconsistent with the idea of a right-hemispheric dominance for all kinds of challenging spatial tasks, since response times and accuracy rates showed that the categorical spatial relation task was more difficult than the coordinate task and the cortical activations were overall greater in the left hemisphere than in the right hemisphere.     

Activation in a frontoparietal cortical network underlies individual differences in the performance of an embedded figures task

The Embedded Figures Test (EFT) requires observers to search for a simple geometric shape hidden inside a more complex figure. Surprisingly, performance in the EFT is negatively correlated with susceptibility to illusions of spatial orientation, such as the Roelofs effect. Using fMRI, we previously demonstrated that regions in parietal cortex are involved in the contextual processing associated with the Roelofs task. In the present study, we found that similar parietal regions (superior parietal cortex and precuneus) were more active during the EFT than during a simple matching task. Importantly, these parietal activations overlapped with regions found to be involved during contextual processing in the Roelofs illusion. Additional parietal and frontal areas, in the right hemisphere, showed strong correlations between brain activity and behavioral performance during the search task. We propose that the posterior parietal regions are necessary for processing contextual information across many different, but related visuospatial tasks, with additional parietal and frontal regions serving to coordinate this processing in participants proficient in the task.     

Exploring the Relationship between Semantics and Space

The asymmetric distribution of human spatial attention has been repeatedly documented in both patients and healthy controls. Biases in the distribution of attention and/or in the mental representation of space may also affect some aspects of language processing. We investigated whether biases in attention and/or mental representation of space affect semantic representations. In particular, we investigated whether semantic judgments could be modulated by the location in space where the semantic information was presented and the role of the left and right parietal cortices in this task. Healthy subjects were presented with three pictures arranged horizontally (one middle and two outer pictures) of items belonging to the same semantic category. Subjects were asked to indicate the spatial position in which the semantic distance between the outer and middle pictures was smaller. Subjects systematically overestimated the semantic distance of items presented in the right side of space. We explored the neural correlates underpinning this bias using rTMS over the left and right parietal cortex. rTMS of the left parietal cortex selectively reduced this rightward bias. Our findings suggest the existence of an attentional and/or mental representational bias in semantic judgments, similar to that observed for the processing of space and numbers. Spatial manipulation of semantic material results in the activation of specialised attentional resources located in the left hemisphere.     

Microstructural Damage of the Posterior Corpus Callosum Contributes to the Clinical Severity of Neglect

One theory to account for neglect symptoms in patients with right focal damage invokes a release of inhibition of the right parietal cortex over the left parieto-frontal circuits, by disconnection mechanism. This theory is supported by transcranial magnetic stimulation studies showing the existence of asymmetric inhibitory interactions between the left and right posterior parietal cortex, with a right hemispheric advantage. These inhibitory mechanisms are mediated by direct transcallosal projections located in the posterior portions of the corpus callosum. The current study, using diffusion imaging and tract-based spatial statistics (TBSS), aims at assessing, in a data-driven fashion, the contribution of structural disconnection between hemispheres in determining the presence and severity of neglect. Eleven patients with right acute stroke and 11 healthy matched controls underwent MRI at 3T, including diffusion imaging, and T1-weighted volumes. TBSS was modified to account for the presence of the lesion and used to assess the presence and extension of changes in diffusion indices of microscopic white matter integrity in the left hemisphere of patients compared to controls, and to investigate, by correlation analysis, whether this damage might account for the presence and severity of patients'' neglect, as assessed by the Behavioural Inattention Test (BIT). None of the patients had any macroscopic abnormality in the left hemisphere; however, 3 cases were discarded due to image artefacts in the MRI data. Conversely, TBSS analysis revealed widespread changes in diffusion indices in most of their left hemisphere tracts, with a predominant involvement of the corpus callosum and its projections on the parietal white matter. A region of association between patients'' scores at BIT and brain FA values was found in the posterior part of the corpus callosum. This study strongly supports the hypothesis of a major role of structural disconnection between the right and left parietal cortex in determining ‘neglect’.     

Disorders of System Brain Activity in Children with Motor (Expressive) Alalia

Motor alalia refers to a number of disorders of expressive speech that are caused by the dysfunction of cerebral structures in the period when the formation of the speech system is not complete. This form of speech disorder is considered as a language disorder characterized by a persistent disturbance of the assimilation of a system of linguistic units. The possible cause of deviations in the development of speech function in children is a disproportion in the levels of development of speech structures in the left and right hemispheres, and this temporary dominance is often associated with an increased activity in the right hemisphere. According to the results of electroencephalographic studies, in children aged five to six years, there are two types of changes of the bioelectric potential system interaction of the brain cortex. The disorders of the spatial organization of interregional EEG correlations are more pronounced in either the left or right hemispheres of the brain. Thus, motor alalia can be accompanied either by disturbances in the interaction between Broca’s and Wernicke’s areas of the left hemisphere, or between symmetrical areas of the right hemisphere.     

Motor learning in man: A review of functional and clinical studies

This chapter reviews results of clinical and functional imaging studies which investigated the time-course of cortical and subcortical activation during the acquisition of motor a skill. During the early phases of learning by trial and error, activation in prefrontal areas, especially in the dorsolateral prefrontal cortex, is has been reported. The role of these areas is presumably related to explicit working memory and the establishment of a novel association between visual cues and motor commands. Furthermore, motor associated areas of the right hemisphere and distributed cerebellar areas reveal strong activation during the early motor learning. Activation in superior-posterior parietal cortex presumably arises from visuospatial processes, while sensory feedback is coded in the anterior-inferior parietal cortex and the neocerebellar structures. With practice, motor associated areas of the left-hemisphere reveal increased activity. This shift to the left hemisphere has been observed regardless of the hand used during training, indicating a left-hemispheric dominance in the storage of visuomotor skills. Concerning frontal areas, learned actions of sequential character are represented in the caudal part of the supplementary motor area (SMA proper), whereas the lateral premotor cortex appears to be responsible for the coding of the association between visuo-spatial information and motor commands. Functional imaging studies which investigated the activation patterns of motor learning under implicit conditions identified for the first, a motor circuit which includes lateral premotor cortex and SMA proper of the left hemisphere and primary motor cortex, for the second, a cognitive loop which consists of basal ganglia structures of the right hemisphere. Finally, activity patterns of intermanual transfer are discussed. After right-handed training, activity in motor associated areas maintains during performance of the mirror version, but is increased during the performance of the original-oriented version with the left hand. In contrary, increased activity during the mirror reversed action, but not during the original-oriented performance of the untrained right hand is observed after left-handed training. These results indicate the transfer of acquired right-handed information which reflects the mirror symmetry of the body, whereas spatial information is mainly transferred after left-handed training. Taken together, a combined approach of clinical lesion studies and functional imaging is a promising tool for identifying the cerebral regions involved in the process of motor learning and provides insight into the mechanisms underlying the generalisation of actions.     

Role of the Right- and Left-Hemispheric Structures in Speech and Memory Formation in Children

The role of structures of the left and right cerebral hemispheres in formation of speech function and memory was studied on the basis of complex examination of children with developmental speech disorders. On the basis of EEG estimation of the functional state of the brain, children were classified in two groups depending on the side of localization of changes in electrical activity: those with local changes in electrical activity in the left hemisphere (group I) and those with changes in the right hemisphere (group II). The medical history suggested that the observed features of topography of local changes in electrical activity were linked with the character of prenatal and labor complications and their consequences leading to embryo- and ontogenetic disorders in development of different brain regions. Comparison of the results of neuropsychological examination of the two groups showed that different regions of the brain cortex of both the left and right hemispheres are involved in speech formation. However, a specific role of the right hemisphere in formation and actualization of automatic speech series was revealed. It was suggested that the integrity of gnostic functions of the right hemisphere and, primarily, the spatial organization of perception and movements is a necessary factor of development of auditory–speech and nominative memory.     

Cerebral Activations Related to Writing and Drawing with Each Hand

BackgroundWriting is a sequential motor action based on sensorimotor integration in visuospatial and linguistic functional domains. To test the hypothesis of lateralized circuitry concerning spatial and language components involved in such action, we employed an fMRI paradigm including writing and drawing with each hand. In this way, writing-related contributions of dorsal and ventral premotor regions in each hemisphere were assessed, together with effects in wider distributed circuitry. Given a right-hemisphere dominance for spatial action, right dorsal premotor cortex dominance was expected in left-hand writing while dominance of the left ventral premotor cortex was expected during right-hand writing.MethodsSixteen healthy right-handed subjects were scanned during audition-guided writing of short sentences and simple figure drawing without visual feedback. Tapping with a pencil served as a basic control task for the two higher-order motor conditions. Activation differences were assessed with Statistical Parametric Mapping (SPM).ResultsWriting and drawing showed parietal-premotor and posterior inferior temporal activations in both hemispheres when compared to tapping. Drawing activations were rather symmetrical for each hand. Activations in left- and right-hand writing were left-hemisphere dominant, while right dorsal premotor activation only occurred in left-hand writing, supporting a spatial motor contribution of particularly the right hemisphere. Writing contrasted to drawing revealed left-sided activations in the dorsal and ventral premotor cortex, Broca’s area, pre-Supplementary Motor Area and posterior middle and inferior temporal gyri, without parietal activation.DiscussionThe audition-driven postero-inferior temporal activations indicated retrieval of virtual visual form characteristics in writing and drawing, with additional activation concerning word form in the left hemisphere. Similar parietal processing in writing and drawing pointed at a common mechanism by which such visually formatted information is used for subsequent sensorimotor integration along a dorsal visuomotor pathway. In this, the left posterior middle temporal gyrus subserves phonological-orthographical conversion, dissociating dorsal parietal-premotor circuitry from perisylvian circuitry including Broca''s area.     

Changes in the spatial organization of cortical electrical activity during increasing working memory load

Analysis of EEG coherence performed in 60 healthy adult subjects revealed some changes in the spatial organization of cortical electrical activity produced by complication of the context of cognitive performance (increasing the working memory load). Changes in the degree of coherence of cortical potentials within the local areas were observed already at the stage of the "operative readiness" immediately after the instruction, i.e., representation of the cognitive task sequence in the explicit working memory. The observed changes were different in the anterior (decrease in the degree of coherence) and posterior (increase in coherence) areas of the cortex. Context-related increase in the local coherence was more pronounced in the temporal, parietal, and occipital areas of the left hemisphere than in the right hemisphere.     

Modality-specific control of strategic spatial attention in parietal cortex

The neural basis of selective spatial attention presents a significant challenge to cognitive neuroscience. Recent neuroimaging studies have suggested that regions of the parietal and temporal cortex constitute a "supramodal" network that mediates goal-directed attention in multiple sensory modalities. Here we used transcranial magnetic stimulation (TMS) to determine which cortical subregions control strategic attention in vision and touch. Healthy observers undertook an orienting task in which a central arrow cue predicted the location of a subsequent visual or somatosensory target. To determine the attentional role of cortical subregions at different stages of processing, TMS was delivered to the right hemisphere during cue or target events. Results indicated a critical role of the inferior parietal cortex in strategic orienting to visual events, but not to somatosensory events. These findings are inconsistent with the existence of a supramodal attentional network and instead provide direct evidence for modality-specific attentional processing in parietal cortex.     

Asymmetry of the transcallosal responses in the parietal cortex of kittens in the 1st month of life

In acute experiments on kittens the process of formation of asymmetry of transcallosal responses (TCR) was studied in multiple leads from symmetrical points of the parietal cortex. By the early positive-negative TCR complex, vanishing as a result of callosotomy, predominance of positive components in the right hemisphere was found in 2-7 days kittens, whereas in 8-24 days animals the left hemisphere dominated by both phases of responses. By the late TCR component preserved after section of the callosal body, left-hemispheric asymmetry was found in the elder group of kittens; it was absent in the younger animals. TCR asymmetry in the parietal cortex depended on the sex of the animals. With their age its inversion and enhancement took place. This process is based on the increase of TCR amplitude in the left hemisphere, with no increase in the right hemisphere.     

Activation of the parieto-premotor network is associated with vivid motor imagery--a parametric FMRI study

The present study examined the neural basis of vivid motor imagery with parametrical functional magnetic resonance imaging. 22 participants performed motor imagery (MI) of six different right-hand movements that differed in terms of pointing accuracy needs and object involvement, i.e., either none, two big or two small squares had to be pointed at in alternation either with or without an object grasped with the fingers. After each imagery trial, they rated the perceived vividness of motor imagery on a 7-point scale. Results showed that increased perceived imagery vividness was parametrically associated with increasing neural activation within the left putamen, the left premotor cortex (PMC), the posterior parietal cortex of the left hemisphere, the left primary motor cortex, the left somatosensory cortex, and the left cerebellum. Within the right hemisphere, activation was found within the right cerebellum, the right putamen, and the right PMC. It is concluded that the perceived vividness of MI is parametrically associated with neural activity within sensorimotor areas. The results corroborate the hypothesis that MI is an outcome of neural computations based on movement representations located within motor areas.     

Changes in electrical brain activity in patients with panic disorders

Brain electrical activity was recorded in 38 patients with typical and in 42 patients with atypical panic disorders, also in 30 normal controls. Compared to controls, patients both with typical and with atypical panic disorders differed significantly in reduced spectral power of the EEG alpha band in the right hemisphere. Moreover, in patients with typical panic disorders, the spectral power of the EEG beta1 band was increased in the frontal, temporal, central, and parietal areas of the right hemisphere. In patients with atypical panic disorders, the spectral power of the theta band was increased in the temporal areas of the right hemisphere. The changes in the EEG activity in patients with typical panic disorders are supposed to reflect an increase in activity of non-specific systems of the mesencephalic reticular formation, and the EEG changes in patients with atypical panic attacks may be associated with increased activity of the temporolimbic brain structures.     

Features of EEG in patients with disorders due to psychoactive substance use during olfactory stimulation

Electroencephalographic (EEG) spectra have been analyzed under baseline conditions and during olfactory stimulation in substance-dependent and healthy subjects. The intergroup differences in the EEG spectra resulting from an increase in the power of cortical bioelectric potentials in patients with disorders due to psychoactive substance use were recorded in the parietal and temporal EEG leads. Interhemispheric differences have been found in the contribution of different frequencies to the spectral characteristics of the EEG. In patients with addictive disorders, in the temporal area of the left hemisphere, in the high-frequency range, a significant increase in the power of bioelectric potentials was recorded under baseline conditions and during olfactory stimulation. An increased power of α activity was typical of the temporal area of the right hemisphere in patients with disorders due to psychoactive substance use compared to the healthy subjects. The neurophysiological patterns found may be related to the psychological and behavioral features of addictive disorders.     

The role of the posterior parietal cortex in coordinate transformations for visual-motor integration

Lesion to the posterior parietal cortex in monkeys and humans produces spatial deficits in movement and perception. In recording experiments from area 7a, a cortical subdivision in the posterior parietal cortex in monkeys, we have found neurons whose responses are a function of both the retinal location of visual stimuli and the position of the eyes in the orbits. By combining these signals area 7 a neurons code the location of visual stimuli with respect to the head. However, these cells respond over only limited ranges of eye positions (eye-position-dependent coding). To code location in craniotopic space at all eye positions (eye-position-independent coding) an additional step in neural processing is required that uses information distributed across populations of area 7a neurons. We describe here a neural network model, based on back-propagation learning, that both demonstrates how spatial location could be derived from the population response of area 7a neurons and accurately accounts for the observed response properties of these neurons.     

Maps of space in human frontoparietal cortex

Prefrontal cortex (PFC) and posterior parietal cortex (PPC) are neural substrates for spatial cognition. We here review studies in which we tested the hypothesis that human frontoparietal cortex may function as a priority map. According to priority map theory, objects or locations in the visual world are represented by neural activity that is proportional to their attentional priority. Using functional magnetic resonance imaging (fMRI), we first identified topographic maps in PFC and PPC as candidate priority maps of space. We then measured fMRI activity in candidate priority maps during the delay periods of a covert attention task, a spatial working memory task, and a motor planning task to test whether the activity depended on the particular spatial cognition. Our hypothesis was that some, but not all, candidate priority maps in PFC and PPC would be agnostic with regard to what was being prioritized, in that their activity would reflect the location in space across tasks rather than a particular kind of spatial cognition (e.g., covert attention). To test whether patterns of delay period activity were interchangeable during the spatial cognitive tasks, we used multivariate classifiers. We found that decoders trained to predict the locations on one task (e.g., working memory) cross-predicted the locations on the other tasks (e.g., covert attention and motor planning) in superior precentral sulcus (sPCS) and in a region of intraparietal sulcus (IPS2), suggesting that these patterns of maintenance activity may be interchangeable across the tasks. Such properties make sPCS in frontal cortex and IPS2 in parietal cortex viable priority map candidates, and suggest that these areas may be the human homologs of the monkey frontal eye field (FEF) and lateral intraparietal area (LIP).     

Spatial frames of reference and somatosensory processing: a neuropsychological perspective.

In patients with lesions in the right hemisphere, frequently involving the posterior parietal regions, left-sided somatosensory (and visual and motor) deficits not only reflect a disorder of primary sensory processes, but also have a higher-order component related to a defective spatial representation of the body. This additional factor, related to right brain damage, is clinically relevant: contralesional hemianaesthesia (and hemianopia and hemiplegia) is more frequent in right brain-damaged patients than in patients with damage to the left side of the brain. Three main lines of investigation suggest the existence of this higher-order pathological factor. (i) Right brain-damaged patients with left hemineglect may show physiological evidence of preserved processing of somatosensory stimuli, of which they are not aware. Similar results have been obtained in the visual domain. (ii) Direction-specific vestibular, visual optokinetic and somatosensory or proprioceptive stimulations may displace spatial frames of reference in right brain-damaged patients with left hemineglect, reducing or increasing the extent of the patients'' ipsilesional rightward directional error, and bring about similar directional effects in normal subjects. These stimulations, which may improve or worsen a number of manifestations of the neglect syndrome (such as extrapersonal and personal hemineglect), have similar effects on the severity of left somatosensory deficits (defective detection of tactile stimuli, position sense disorders). However, visuospatial hemineglect and the somatosensory deficits improved by these stimulations are independent, albeit related, disorders. (iii) The severity of left somatosensory deficits is affected by the spatial position of body segments, with reference to the midsagittal plane of the trunk. A general implication of these observations is that spatial (non-somatotopic) levels of representation contribute to corporeal awareness. The neural basis of these spatial frames includes the posterior parietal and the premotor frontal regions. These spatial representations could provide perceptual-premotor interfaces for the organization of movements (e.g. pointing, locomotion) directed towards targets in personal and extrapersonal space. In line with this view, there is evidence that the sensory stimulations that modulate left somatosensory deficits affect left motor disorders in a similar, direction-specific, fashion.     

Anatomical brain asymmetry in monkeys: frontal, temporoparietal, and limbic cortex in Macaca

Measurements evaluating possible cerebral hemispheric asymmetries were taken by hand on frontal, parietal, and temporal cortex on 60 formalin-fixed Macaca mulatta and Macaca fascicularis brain specimens. No statistically significant (P less than 0.05) right/left side differences in the mean length of four sulci in visual-processing areas of the cortex were found. The sulcus adjacent to the region cytoarchitecturally homologous to the motor speech area in the human brain did not show pronounced asymmetry. In both species, however, a small parietal lobe sulcus showed greater development on the left hemisphere than in the right. In measurements made using digital planimetry, right/left side differences in the area of the dorsal cingulate gyrus were not found. Behavioral evidence suggests that monkeys do not exhibit a consistent pattern of cerebral dominance for functions associated with most of these regions of the brain.     

Spatial orientation and the representation of space with parietal lobe lesions.

Damage to the human parietal cortex leads to disturbances of spatial perception and of motor behaviour. Within the parietal lobe, lesions of the superior and of the inferior lobule induce quite different, characteristic deficits. Patients with inferior (predominantly right) parietal lobe lesions fail to explore the contralesional part of space by eye or limb movements (spatial neglect). In contrast, superior parietal lobe lesions lead to specific impairments of goal-directed movements (optic ataxia). The observations reported in this paper support the view of dissociated functions represented in the inferior and the superior lobule of the human parietal cortex. They suggest that a spatial reference frame for exploratory behaviour is disturbed in patients with neglect. Data from these patients'' visual search argue that their failure to explore the contralesional side is due to a disturbed input transformation leading to a deviation of egocentric space representation to the ipsilesional side. Data further show that this deviation follows a rotation around the earth-vertical body axis to the ipsilesional side rather than a translation towards that side. The results are in clear contrast to explanations that assume a lateral gradient ranging from a minimum of exploration in the extreme contralesional to a maximum in the extreme ipsilesional hemispace. Moreover, the failure to orient towards and to explore the contralesional part of space appears to be distinct from those deficits observed once an object of interest has been located and releases reaching. Although patients with neglect exhibit a severe bias of exploratory movements, their hand trajectories to targets in peripersonal space may follow a straight path. This result suggests that (i) exploratory and (ii) goal-directed behaviour in space do not share the same neural control mechanisms. Neural representation of space in the inferior parietal lobule seems to serve as a matrix for spatial exploration and for orienting in space but not for visuomotor processes involved in reaching for objects. Disturbances of such processes rather appear to be prominent in patients with more superior parietal lobe lesions and optic ataxia.