A fronto-parietal circuit for object manipulation in man: evidence from an fMRI-study

Functional magnetic resonance imaging (fMRI) was used to localize brain areas active during manipulation of complex objects. In one experiment subjects were required to manipulate complex objects for exploring their macrogeometric features as compared to manipulation of a simple smooth object (a sphere). In a second experiment subjects were asked to manipulate complex objects and to silently name them upon recognition as compared to manipulation of complex not recognizable objects without covert naming. Manipulation of complex objects resulted in an activation of ventral premotor cortex [Brodmann's area (BA) 44], of a region in the intraparietal sulcus (most probably corresponding to the anterior intraparietal area in the monkey), of area SII and of a sector of the superior parietal lobule. When the objects were covertly named additional activations were found in the opercular part of BA 44 and in the pars triangularis of the inferior frontal gyrus (BA 45). We suggest that a fronto-parietal circuit for manipulation of objects exists in humans and involves basically the same areas as in the monkey. It is proposed that area SII analyses the intrinsic object characteristics whilst the superior parietal lobule is related to kinaesthesia.     

The role of human left superior parietal lobule in body part localization

Electrophysiological data in primates suggest that the superior parietal lobule integrates the position of the limbs to construct complex representations of postures. Although in humans the neural basis of these mechanisms remains largely unknown, neuropsychological studies have implicated left superior parietal regions. We devised a simple functional magnetic resonance imaging paradigm aimed at exploring this hypothesis in healthy humans. Strong activation was obtained within the left but not the right superior parietal lobule, providing additional evidence that this structure may play a key role in body part localization processing.     

Motor sequence complexity and performing hand produce differential patterns of hemispheric lateralization

Studies in brain damaged patients conclude that the left hemisphere is dominant for controlling heterogeneous sequences performed by either hand, presumably due to the cognitive resources involved in planning complex sequential movements. To determine if this lateralized effect is due to asymmetries in primary sensorimotor or association cortex, whole-brain functional magnetic resonance imaging was used to measure differences in volume of activation while healthy right-handed subjects performed repetitive (simple) or heterogeneous (complex) finger sequences using the right or left hand. Advanced planning, as evidenced by reaction time to the first key press, was greater for the complex than simple sequences and for the left than right hand. In addition to the expected greater contralateral activation in the sensorimotor cortex (SMC), greater left hemisphere activation was observed for left, relative to right, hand movements in the ipsilateral left superior parietal area and for complex, relative to simple, sequences in the left premotor and parietal cortex, left thalamus, and bilateral cerebellum. No such volumetric asymmetries were observed in the SMC. Whereas the overall MR signal intensity was greater in the left than right SMC, the extent of this asymmetry did not vary with hand or complexity level. In contrast, signal intensity in the parietal and premotor cortex was greater in the left than right hemisphere and for the complex than simple sequences. Signal intensity in the caudal anterior cerebellum was greater bilaterally for the complex than simple sequences. These findings suggest that activity in the SMC is associated with execution requirements shared by the simple and complex sequences independent of their differential cognitive requirements. In contrast, consistent with data in brain damaged patients, the left dorsal premotor and parietal areas are engaged when advanced planning is required to perform complex motor sequences that require selection of different effectors and abstract organization of the sequence, regardless of the performing hand.     

Coding complexity in the human motor circuit

Cortical oscillatory dynamics are known to be critical for human movement, although their functional significance remains unclear. In particular, there is a strong beta (15–30 Hz) desynchronization that begins before movement onset and continues during movement, before rebounding after movement termination. Several studies have connected this response to motor planning and/or movement selection operations, but to date such studies have examined only the early aspects of the response (i.e., before movement) and a limited number of parameters. In this study, we used magnetoencephalography (MEG) and a novel motor sequence paradigm to probe how motor plan complexity modulates peri‐movement beta oscillations, and connectivity within activated circuits. We also examined the dynamics by imaging beta activity before and during movement execution and extracting virtual sensors from key regions. We found stronger beta desynchronization during complex relative to simple sequences in the right parietal and left dorsolateral prefrontal cortex (DLPFC) during movement execution. There was also an increase in functional connectivity between the left DLPFC and right parietal shortly after movement onset during complex but not simple sequences, which produced a significant conditional effect (i.e., complex > simple) that was not attributable to differences in response amplitude. This study is the first to demonstrate that complexity modulates the dynamics of the peri‐movement beta ERD, which provides crucial new data on the functional role of this well‐known oscillatory motor response. These data further suggest that execution of complex motor behavior may recruit key regions of the fronto‐parietal network, in addition to traditional sensorimotor regions. Hum Brain Mapp 36:5155–5167, 2015. © 2015 Wiley Periodicals, Inc.     

Projections of the parietal cortex on the vestibular complex in Macaca

Connections of parietal cortex (especially posterior part of area 7) with subcortical structures related with vestibular function were examined in four monkeys (Macaca Fascicularis), by means of anterograde labeling with HRP and tritated amino-acids tracers. Posterior parietal cortex was found to have direct efferent projections onto vestibular nuclei complex and prepositus hypoglossi nucleus. These efferences were distributed bilaterally with an ipsilateral preponderance. The labeled terminals were organized in precise patterns in vestibular nuclei in such a way that two groups of cortical efferences could be distinguished: the first one terminates on vestibular nuclei related with the cervico-spinal motor system and the second one terminates on both prepositus hypoglossi nucleus and vestibular nuclei involved in vestibulo-ocular functions. These latter efferent projections of parietal cortex onto vestibular nuclei complex could account for the role played by the posterior part of area 7 in the modulation of the vestibulo-ocular reflex.     

The role of the lateral intraparietal area in orienting attention and its implications for visual search

Orienting visual attention is of fundamental importance when viewing a visual scene. One of the areas thought to play a role in the guidance of this process is the posterior parietal cortex. In this review, we will describe the way the lateral intraparietal area (LIP) of the posterior parietal cortex acts as a priority map to help guide the allocation of covert attention and eye movements (overt attention). We will explain the concept of a priority map and then show that LIP activity is biased by both bottom-up stimulus-driven factors and top-down cognitive influences, and that this activity can be used to predict the locus of covert attention and initial saccadic latencies in simple visual search tasks. We will then describe evidence for how this system acts during covert visual search and how its activity could be used to optimize overt visual search performance.     

Distinct cortical networks support the planning and online control of reaching-to-grasp in humans

A number of brain imaging studies have identified regions involved in the planning and control of complex actions. Here we attempt to contrast activity related to planning and online control in the human brain during simple reaching and grasping movements. In four conditions, participants did one of the following: passively observed a grasp target; planned a grasping movement without executing; planned and then executed a grasp; or immediately executed a grasp. Neural activity was measured using functional magnetic resonance imaging and activity in the various conditions compared. Two large, independent networks of brain activity were identified: (i) a planning network including the premotor cortex, basal ganglia, anterior cingulate, posterior medial parietal area, superior parietal occipital cortex and middle intraparietal sulcus; and (ii) a control network including sensorimotor cortex, the cerebellum, the supramarginal gyrus and the superior parietal lobule. These findings provide evidence that the planning and control of even simple reaching and grasping actions use different brain regions, including different parts of the frontal and parietal lobes.     

The attentional role of the left parietal cortex: the distinct lateralization and localization of motor attention in the human brain

It is widely agreed that visuospatial orienting attention depends on a network of frontal and parietal areas in the right hemisphere. It is thought that the visuospatial orienting role of the right parietal lobe is related to its role in the production of overt eye movements. The experiments reported here test the possibility that other parietal regions may be important for directing attention in relation to response modalities other than eye movement. Specifically, we used positron emission tomography (PET) to test the hypothesis that a 'left' parietal area, the supramarginal gyrus, is important for attention in relation to limb movements (Rushworth et al., 1997; Rushworth, Ellison, & Walsh, in press). We have referred to this process as 'motor attention' to distinguish it from orienting attention. In one condition subjects spent most of the scanning period covertly attending to 'left' hand movements that they were about to make. Activity in this first condition was compared with a second condition with identical stimuli and movement responses but lacking motor attention periods. Comparison of the conditions revealed that motor attention-related activity was almost exclusively restricted to the 'left' hemisphere despite the fact that subjects only ever made ipsilateral, left-hand responses. Left parietal activity was prominent in this comparison, within the parietal lobe the critical region for motor attention was the supramarginal gyrus and the adjacent anterior intraparietal sulcus (AIP), a region anterior to the posterior parietal cortex identified with orienting attention. In a second part of the experiment we compared a condition in which subjects covertly rehearsed verbal responses with a condition in which they made verbal responses immediately without rehearsal. A comparison of the two conditions revealed verbal rehearsal-related activity in several anterior left hemisphere areas including Broca's area. The lack of verbal rehearsal-related activity in the left supra-marginal gyrus confirms that this area plays a direct role in motor attention that cannot be attributed to any strategy of verbal mediation. The results also provide evidence concerning the importance of ventral premotor (PMv) and Broca's area in motor attention and language processes.     

Effective connectivity of the multiplication network: A functional MRI and multivariate granger causality mapping study

Developmental neuropsychology and functional neuroimaging evidence indicates that simple and complex mental calculation is subserved by a fronto‐parietal network. However, the effective connectivity (connection direction and strength) among regions within the fronto‐parietal network is still unexplored. Combining event‐related fMRI and multivariate Granger Causality Mapping (GCM), we administered a multiplication verification task to healthy participants asking them to solve single and double‐digit multiplications. The goals of our study were first, to identify the effective connectivity of the multiplication network, and second, to compare the effective connectivity patterns between a low and a high arithmetical competence (AC) group. The manipulation of multiplication difficulty revealed a fronto‐parietal network encompassing bilateral intraparietal sulcus (IPS), left pre‐supplementary motor area (PreSMA), left precentral gyrus (PreCG), and right dorsolateral prefrontal cortex (DLPFC). The network was driven by an intraparietal IPS‐IPS circuit hosting a representation of numerical quantity intertwined with a fronto‐parietal DLPFC‐IPS circuit engaged in temporary storage and updating of arithmetic operations. Both circuits received additional inputs from the PreCG and PreSMA playing more of a supportive role in mental calculation. The high AC group compared to the low AC group displayed a greater activation in the right IPS and based its calculation more on a feedback driven intraparietal IPS‐IPS circuit, whereas the low competence group more on a feedback driven fronto‐parietal DLPFC‐IPS circuit. This study provides first evidence that multivariate GCM is a sensitive approach to investigate effective connectivity of mental processes involved in mental calculation and to compare group level performances for different populations. Hum Brain Mapp, 2010. © 2010 Wiley‐Liss, Inc.     

Restricted ocular exploration does not seem to explain simultanagnosia

One major function of parietal cortex is to direct our attention towards salient stimuli. The present data suggest that it also plays an important role in visual gestalt perception. Patients with simultanagnosia following lesions in this area are not able to extract the meaning of a visual scene whereas being perfectly able to recognise individual objects of this scene. We tested two patients with simultanagnosia with hierarchical Navon figures combined with eye movements recordings. The patients' performance allowed us to compare directly the scan paths in trials in which the global letter shape was recognised with trials in which the global letter shape was not recognised. We did not find any obvious differences in the eye movement pattern related to the two perceptual situations. The two patients did not show a significant problem in shifting their eyes (and thus possibly also their attentional focus) to all aspects of the complex visual stimulus when attempting to bind together the different elements of spatially distributed information. The results demonstrate that restricted ocular exploration cannot be the reason for the patients' inability to recognise the global shape of stimuli. Our data rather suggest a role of parietal cortex in visual gestalt perception that is beyond its role of directing attention towards relevant objects.     

Ictal abdominal pain heralding parietal lobe haemorrhage.

We present an unusual case of ictal abdominal pain occurring in the setting of parietal lobe haemorrhage. The role of the somatosensory area I in pain perception is postulated.     

Dissociation of subtraction and multiplication in the right parietal cortex: evidence from intraoperative cortical electrostimulation

Previous research has consistently shown that the left parietal cortex is critical for numerical processing, but the role of the right parietal lobe has been much less clear. This study used the intraoperative cortical electrical stimulation approach to investigate neural dissociation in the right parietal cortex for subtraction and multiplication. Results showed that multiplication (as well as picture naming) was not affected by the cortical electrical stimulation on all the targeted sites of the right parietal cortex as well as those of the right temporal cortex. In contrast, stimulation at three right parietal sites (two sites in the right inferior parietal lobule and one in the right angular gyrus) impaired performance on simple subtraction problems. This study provided the first evidence from an intraoperative cortical electrical stimulation study to show the dissociation of arithmetic operations in the right parietal cortex. This dissociation between subtraction and multiplication suggests that the right parietal cortex plays a more significant role in quantity processing (subtraction) than in verbal processing (multiplication) in numerical processing.     

Simple and complex vestibular responses induced by electrical cortical stimulation of the parietal cortex in humans

The present study reports on a patient undergoing invasive monitoring for intractable epilepsy who experienced different vestibular sensations after electrical cortical stimulation of the inferior parietal lobule at the anterior part of the intraparietal sulcus. Types of vestibular response ranged from simple to complex sensations and depended on stimulation site and applied current. The findings suggest vestibular topography and hierarchical processing within the parietal vestibular cortex of humans.     

Posterior parietal mechanisms of visual attention

The posterior parietal cortex plays an important role in visual-spatial attention. Imaging studies reveal consistent parietal activation in attention tasks, while lesions to this area produce significant perceptual deficits. Non-human primate models have been particularly informative in investigating the neurophysiology of attention. The activity of posterior parietal neurons to the same operant stimuli is modulated by whether they are attended or not based on prior information, or whether they attract attention by virtue of their saliency. Posterior parietal neuronal activity appears to provide critical information for shifting attention between stimuli and spatial locations.     

The role of the parietal cortex in visual attention--hemispheric asymmetries and the effects of learning: a magnetic stimulation study

Our previous studies of the role of the parietal cortex in visual learning and attention showed that the right parietal cortex is required for normal performance on conjunction visual search tasks but that its role depends on whether subjects are naive or trained on the task. Here we extend these findings in two Experiments. Experiment 1 shows that magnetic stimulation of the left parietal cortex also impairs performance (measured as reaction time) on conjunction visual search tasks, but only when the target is present in the right (contralateral) visual field. Stimulation of the same region on a feature detection task speeds up performance significantly when the target is in the left (ipsilateral) visual field. Experiment 2 explores further the role of the right parietal cortex in learning conjunction search tasks. Stimulation of the right parietal cortex in subjects who had already trained on some visual search tasks did not impair performance on a novel motion/form conjunction task even though the search was clearly serial. Stimulation of area V5, however, severely disrupted performance on the same task. These data indicate that the role of the parietal cortex may change much earlier in the course of training than initially thought.     

Model-driven neuromodulation of the right posterior region promotes encoding of long-term memories

BackgroundLong-term recognition memory depends both on initial encoding and on subsequent recognition processes.ObjectiveIn this study we aimed at improving long-term memory by modulating posterior parietal brain activity during the encoding process. If this area is causally involved in memory encoding, its facilitation should lead to behavioral improvement. Based on the dual-process memory framework, we also expected that the neuromodulation would dissociate subsequent familiarity-based and recollection-based recognition.MethodsWe investigated the role of the posterior parietal brain oscillations in facial memory formation in three separate experiments using electroencephalography (EEG), functional magnetic resonance imaging (fMRI), and model-driven, multi-electrode transcranial alternating current stimulation (tACS).ResultsUsing fMRI and EEG, we confirmed that the right posterior parietal cortex is an essential node that promotes the encoding of long-term memories. We found that single-trial low theta power in this region predicts subsequent long-term recognition. On this basis, we fine-tuned the spatial and frequency settings of tACS during memory encoding. Model-driven tACS over the right posterior brain area augmented subsequent long-term recognition memory and particularly the familiarity of the observed stimuli. The recollection process, and short-term task performance as control remained unchanged. Control stimulation over the left hemisphere had no behavioral effect.ConclusionWe conclude that the right posterior brain area is crucial in long-term memory encoding.     

Corticocortical connections of visual, sensorimotor, and multimodal processing areas in the parietal lobe of the macaque monkey

We studied the corticocortical connections of architectonically defined areas of parietal and temporoparietal cortex, with emphasis on areas in the intraparietal sulcus (IPS) that are implicated in visual and somatosensory integration. Retrograde tracers were injected into selected areas of the IPS, superior temporal sulcus, and parietal lobule. The distribution of labeled cells was charted in relation to architectonically defined borders throughout the hemisphere and displayed on computer-generated three-dimensional reconstructions and on cortical flat maps. Injections centered in the ventral intraparietal area (VIP) revealed a complex pattern of inputs from numerous visual, somatosensory, motor, and polysensory areas, and from presumed vestibular- and auditory-related areas. Sensorimotor projections were predominantly from the upper body representations of at least six somatotopically organized areas. In contrast, injections centered in the neighboring ventral lateral intraparietal area (LIPv) revealed inputs mainly from extrastriate visual areas, consistent with previous studies. The pattern of inputs to LIPv largely overlapped those to zone MSTdp, a newly described subdivision of the medial superior temporal area. These results, in conjunction with those from injections into other parietal areas (7a, 7b, and anterior intraparietal area), support the fine-grained architectonic partitioning of cortical areas described in the preceding study. They also support and extend previous evidence for multiple distributed networks that are implicated in multimodal integration, especially with regard to area VIP.     

Cortical mechanism underlying externally cued gait initiation studied by contingent negative variation

In order to clarify the cortical mechanism underlying gait initiation, we examined the scalp distribution of the contingent negative variation (CNV) preceding externally cued gait initiation in a simple reaction-time paradigm in 10 healthy right-handed men, and compared the results with the CNV preceding simple foot dorsiflexion. A pair of auditory stimuli was given with an interstimulus (S1–S2) interval of 2 s and gait consisting of at least 3 steps was initiated with the right footstep as fast as possible in response to S2. Brisk dorsiflexion of the right foot was employed as a control task. It was found that the late CNV in the gait initiation task started about 1 s before S2, and was largest at Cz (−9.3 ± 3.1 μV) without clear asymmetry over the scalp. However, it was ill defined in the parietal area. In the foot dorsiflexion task, the late CNV was maximal at Cz (−7.1 ± 2.9 μV), and clearly seen also over the parietal area. The late CNV at Cz was significantly (P < 0.01) larger in the gait initiation than in the simple foot dorsiflexion. The amplitude of the late CNV preceding the foot dorsiflexion task was not significantly different between the sitting and the standing posture. In view of the results of previous invasive studies in both humans and animals which showed some frontal areas, including the supplementary motor area (SMA) and the primary motor cortex, as the generators of the late CNV, it is suggested that the cerebral cortex is active in initiation of externally triggered gait in a different way from the simple foot movement, and that bilateral SMAs may play a more important role in gait initiation than in simple foot movement.     

Cells in somatosensory areas show synchrony with beta oscillations in monkey motor cortex

Oscillatory synchronization between somatosensory and motor cortex has previously been reported using field potential recordings, but interpretation of such results can be confounded by volume conduction. We examined coherence between single-unit discharge in somatosensory/parietal areas and local field potential from the same area as the unit, or from the motor cortex, in two macaque monkeys trained to perform a finger movement task. There were clear coherence peaks at approximately 17.5 Hz for cells in the primary somatosensory cortex (both proprioceptive and cutaneous areas) and posterior parietal cortex (area 5). The size of coherence in all areas was comparable to previous reports analysing motor cortical cells and M1 field potentials. Many coherence phases clustered around -pi/2 radians, indicating zero lag synchronization of parietal cells with M1 oscillatory activity. These results indicate that cells in somatosensory and parietal areas have information about the presence of oscillations in the motor system. Such oscillatory coupling across the central sulcus may play an important role in sensorimotor integration of both proprioceptive and cutaneous signals.