Activity In Posterior Parietal Cortex Research Articles

Cortical Temporal Dynamics of Visually Guided Behavior

Little is known about the temporal dynamics of cortical activation during visually guided behavior. We measured changes in brain activity in human posterior parietal cortex (PPC) and premotor cortex (PMC) during saccades and visually guided reaching using magnetoencephalography (MEG) and novel time-frequency reconstructions of MEG (tfMEG) data. Results indicate that early high-gamma activity over the frontal eye fields (FEFs) was present during saccade preparation, and high-gamma activity progressed from the supplementary and FEFs to visual cortex during saccade execution. In contrast, early high-gamma activity over dorsal PMC and late beta activity in primary motor cortex and PPC were unique to reach preparation. During reaching, high-gamma activity progressed from sensorimotor cortex and PMC to parietooccipital cortex. These unique spatial-temporal processing patterns reflect the known connectivity of 2 different sensorimotor networks in macaques. The onset and duration of activity in these areas provides direct evidence for concurrent serial and parallel processing in the human brain during the integration of the sensorimotor inputs necessary for visually guided performance.

MR‐compatible device for monitoring hand tracing and writing tasks in fMRI with an application to healthy subjects

AbstractMonitoring devices enable control of the correct execution of a given task during functional magnetic resonance imaging (fMRI) acquisitions and analysis of behavioral features that can influence brain activation patterns. In this report, we describe and validate a low‐cost device for monitoring hand tracing and writing tasks during fMRI. The subject holds a light‐emitting pen whose light spot is recorded by a fixed camera aligned with the tracing plane. Pen trajectories are extracted by a blob detection algorithm through Laplacian of Gaussian filtering applied to the camera recordings. Following phantom and in vivo experiments which demonstrated MR compatibility, the device was applied to monitor the particular case of the task of continuous and self‐paced writing of an “8” figure in 10 healthy subjects. They underwent fMRI examinations during the task under three conditions: spontaneous frequency and figure size, “low” frequency and “small” figure size. The task recordings were analyzed with a dedicated algorithm that computed both frequency and area of the figures “8” writing. The device was judged comfortable by all subjects. fMRI data analysis showed that task frequency influenced the activation within primary sensory motor and premotor frontal cortices, while figure size interfered with the activation in posterior parietal cortex. Both frequency and size parameters modulated activation in the inferior cerebellum. By monitoring writing‐tasks executions, this device is expected to broaden the spectrum of applications of fMRI. Indeed, it could allow the investigation of patients suffering from neurological disorders affecting handwriting, such as apraxic disorders, cerebellar disorders, or parkinsonisms. © 2010 Wiley Periodicals, Inc. Concepts Magn Reson Part A 36A: 139–152, 2010.

Posterior parietal cortex activity predicts individual differences in visual short-term memory capacity

Humans show a severe capacity limit in the number of objects they can store in visual short-term memory (VSTM). We recently demonstrated with functional magnetic resonance imaging that VSTM storage capacity estimated in averaged group data correlated strongly with posterior parietal/superior occipital cortex activity (Todd & Marois, 2004). However, individuals varied widely in their VSTM capacity. Here, we examined the neural basis of these individual differences. A voxelwise, individualdifferences analysis revealed a significant correlation between posterior parietal cortex (PPC) activity and individuals’ VSTM storage capacity. In addition, a region-of-interest analysis indicated that other brain regions, particularly visual occipital cortex, may contribute to individual differences in VSTM capacity. Thus, although not ruling out contributions from other brain regions, the individual-differences approach supports a key role for the PPC in VSTM by demonstrating that its activity level predicts individual differences in VSTM storage capacity.

Bending the Rules: Strategic Behavioral Differences Are Reflected in the Brain

The implementation of higher-order conditional motor behavior was investigated in the present fMRI study with the objective of answering three questions: (a) what happens in situations where one stimulus dimension alone does not sufficiently determine the correct response?; (b) does the implementation of second-order stimulus-response (S-R) rules on the basis of matching (congruent) or nonmatching (incongruent) S-R associations differ from the implementation of congruent and incongruent first-order S-R rules?; and (c) is the cerebral implementation of second-order rules influenced by interindividual behavioral differences arising from the use of different strategies? The findings indicate that several cortical areas were more strongly engaged for second-order rules. More specifically, rule integration based on a rule match led to enhanced activation in posterior parietal cortex, whereas rule integration based on a rule mismatch was associated with enhanced activation in dorsal premotor cortex and left rostrolateral prefrontal cortex. Interindividual strategy differences were revealed by strikingly different behavioral data patterns: One subgroup of participants displayed strong congruency effects for second-order rules, whereas another subgroup displayed nonsignificant or even reversed congruency effects. Importantly, these strategy differences strongly modulated the cerebral implementation of second-order rules based on a rule mismatch. Together, the present findings reveal differential brain activation patterns for higher-order S-R rules depending on rule congruency and interindividual strategy differences. Moreover, they emphasize the necessity of taking interindividual behavioral differences into account when investigating the cerebral implementation of cognitive processes even in rather simple and well-controlled experimental paradigms.

PW01-151 - Neural networks for motion processing and pursuit eye movements in untreated first-episode psychosis

ObjectiveTo identify alterations in neural networks for visual motion perception and pursuit tracking and their interrelationship in schizophrenia, and secondarily to evaluate their comparability to findings in psychotic bipolar disorder.MethodsUntreated first-episode patients with schizophrenia (N=24) and psychotic bipolar disorder (N=13), and 20 matched healthy participants performed a passive visual motion processing task and a pursuit eye tracking task, which patients have been shown to perform as well as healthy subjects, during functional neuroimaging. Available subjects were retested after four weeks, during which both patient groups received second generation antipsychotics.ResultsDuring the motion processing task, neither patient group showed reduced activation in V5, but activations in its projection fields in posterior parietal cortex were reduced in both groups. Pursuit related neural activation in both patients groups was not reduced in sensorimotor systems, but was enhanced in anterior intraparietal sulcus and insula. In schizophrenia, activation was also enhanced in dorsolateral prefrontal cortex and dorsomedial thalamus. Greater V5 activation during passive motion processing predicted greater activation in posterior parietal cortex during pursuit in healthy individuals but not in patients. The only significant change at follow-up was decreased anterior cingulate activation during pursuit in schizophrenia.ConclusionsReduced transfer of visual motion information to parietal association cortex may compromise information about target speed and tracking error needed for sensorimotor transformations during pursuit tracking in psychotic disorders. Enhanced activation of a prefrontal-thalamo-parietal network during pursuit tracking in schizophrenia may represent compensation for this deficit.

Long-range coupling of prefrontal cortex and visual (MT) or polysensory (STP) cortical areas in motion perception

Event Abstract Back to Event Long-range coupling of prefrontal cortex and visual (MT) or polysensory (STP) cortical areas in motion perception Lucia M. Vaina1, 2*, Finnegan Calabro1, Fa-Hsuan Lin2 and Matti Hamalainen3 1 Boston University, United States 2 Harvard University, United States 3 Massachusetts General Hospital, United States To investigate how, where and when moving auditory cues interact with the perception of object-motion during self-motion, we conducted psychophysical, and MEG experiments in which the subjects viewed nine textured objects during simulated forward self-motion. On each trial, one object was randomly assigned its own looming motion within the scene. Subjects reported which of four labeled objects had independent motion within the scene in two conditions: (1) visual information only and (2) with additional auditory cue. In psychophysics, observers performed slightly better in the presence of an auditory cue moving in the same direction with the object target (p=0.003, t=4.18, df=8, min 1.2%, and max 8.1). When the auditory cue was static, uninformative, it had not impact on performance. In cortically-constrained MEG source estimates, comparison of the two conditions showed: (i) MT (middle temporal area) activity similar across conditions; (ii) additional activity in the auditory cue condition ventral to MT late after the stimulus presentation; (iii) with the auditory cue, early activity at the right auditory cortex (AC) together with STP (superior temporal polysensory area), (iv) different time courses of these two activities with STP signals later in the epoch together with frontal activity in the right hemisphere, (v) stronger activity in PPC (posterior parietal cortex) in the visual-only condition than in the auditory-cue condition. In addition, Dynamic Granger Causality analysis among cortical regions showed for the auditory cues condition a strong connection of the AC with STP but not with MT suggesting binding of visual and auditory information at STP. Also, while in the visual-only condition PFC is connected with MT, in the auditory-cue condition PFC (prefrontal cortex) is connected to STP. These results indicate that PFC allocates attention to the “object” as a whole, in STP to a moving visual-auditory object, and in MT to a moving visual object. Conference: Biomag 2010 - 17th International Conference on Biomagnetism , Dubrovnik, Croatia, 28 Mar - 1 Apr, 2010. Presentation Type: Poster Presentation Topic: Sensory Processing and Functional Connectivity Citation: Vaina LM, Calabro F, Lin F and Hamalainen M (2010). Long-range coupling of prefrontal cortex and visual (MT) or polysensory (STP) cortical areas in motion perception. Front. Neurosci. Conference Abstract: Biomag 2010 - 17th International Conference on Biomagnetism . doi: 10.3389/conf.fnins.2010.06.00212 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 30 Mar 2010; Published Online: 30 Mar 2010. * Correspondence: Lucia M Vaina, Boston University, Boston, United States, vaina@bu.edu Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Lucia M Vaina Finnegan Calabro Fa-Hsuan Lin Matti Hamalainen Google Lucia M Vaina Finnegan Calabro Fa-Hsuan Lin Matti Hamalainen Google Scholar Lucia M Vaina Finnegan Calabro Fa-Hsuan Lin Matti Hamalainen PubMed Lucia M Vaina Finnegan Calabro Fa-Hsuan Lin Matti Hamalainen Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Activation of right parietal cortex during memory retrieval of nonlinguistic auditory stimuli

In neuroimaging studies, the left ventral posterior parietal cortex (PPC) is particularly active during memory retrieval. However, most studies have used verbal or verbalizable stimuli. We investigated neural activations associated with the retrieval of short, agrammatical music stimuli (Blackwood, 2004), which have been largely associated with right hemisphere processing. At study, participants listened to music stimuli and rated them on pleasantness. At test, participants made old/new recognition judgments with high/low confidence ratings. Right, but not left, ventral PPC activity was observed during the retrieval of these music stimuli. Thus, rather than indicating a special status of left PPC in retrieval, both right and left ventral PPC participate in memory retrieval, depending on the type of information that is to be remembered.

Cortical Temporal Dynamics of Visually Guided Behavior

Little is known about the temporal dynamics of cortical activation during visually guided behavior. We measured changes in brain activity in human posterior parietal cortex (PPC) and premotor cortex (PMC) during saccades and visually guided reaching using magnetoencephalography (MEG) and novel time-frequency reconstructions of MEG (tfMEG) data. Results indicate that early high-gamma activity over the frontal eye fields (FEFs) was present during saccade preparation, and high-gamma activity progressed from the supplementary and FEFs to visual cortex during saccade execution. In contrast, early high-gamma activity over dorsal PMC and late beta activity in primary motor cortex and PPC were unique to reach preparation. During reaching, high-gamma activity progressed from sensorimotor cortex and PMC to parietooccipital cortex. These unique spatial-temporal processing patterns reflect the known connectivity of 2 different sensorimotor networks in macaques. The onset and duration of activity in these areas provides direct evidence for concurrent serial and parallel processing in the human brain during the integration of the sensorimotor inputs necessary for visually guided performance.

Dopamine Transporters in Striatum Correlate with Deactivation in the Default Mode Network during Visuospatial Attention

BackgroundDopamine and dopamine transporters (DAT, which regulate extracellular dopamine in the brain) are implicated in the modulation of attention but their specific roles are not well understood. Here we hypothesized that dopamine modulates attention by facilitation of brain deactivation in the default mode network (DMN). Thus, higher striatal DAT levels, which would result in an enhanced clearance of dopamine and hence weaker dopamine signals, would be associated to lower deactivation in the DMN during an attention task.Methodology/Principal FindingsFor this purpose we assessed the relationship between DAT in striatum (measured with positron emission tomography and [11C]cocaine used as DAT radiotracer) and brain activation and deactivation during a parametric visual attention task (measured with blood oxygenation level dependent functional magnetic resonance imaging) in healthy controls. We show that DAT availability in caudate and putamen had a negative correlation with deactivation in ventral parietal regions of the DMN (precuneus, BA 7) and a positive correlation with deactivation in a small region in the ventral anterior cingulate gyrus (BA 24/32). With increasing attentional load, DAT in caudate showed a negative correlation with load-related deactivation increases in precuneus.Conclusions/SignificanceThese findings provide evidence that dopamine transporters modulate neural activity in the DMN and anterior cingulate gyrus during visuospatial attention. Our findings suggest that dopamine modulates attention in part by regulating neuronal activity in posterior parietal cortex including precuneus (region involved in alertness) and cingulate gyrus (region deactivated in proportion to emotional interference). These findings suggest that the beneficial effects of stimulant medications (increase dopamine by blocking DAT) in inattention reflect in part their ability to facilitate the deactivation of the DMN.

Changes in cerebral activations during movement execution and imagery after parietal cortex TMS interleaved with 3T MRI

The left parietal cortex contributes to goal-directed hand movement. In this study, we targeted this region with transcranial magnetic stimulation (TMS) to assess the effects on a wider distributed circuitry related to motor control. Ten healthy subjects underwent 3 Tesla functional magnetic resonance imaging (fMRI) with interleaved TMS. They either executed or imagined right wrist flexion/extension movements, which was preceded by a 10-second period either with or without TMS. This was applied to the left superior parietal cortex in 10 stimuli of 1 Hz at 115% motor threshold intensity. TMS preceding the movement execution condition resulted in significantly increased activation in the bilateral prefrontal, right temporo-parietal and left posterior parietal cortices, when compared to movement without such intervention ( P < 0.001 voxel-level; P < 0.05, volume corrected). Movement imagery after TMS showed significantly increased activation in the left medial prefrontal cortex, right lateral prefrontal cortex, left supramarginal gyrus and right occipital cortex, while a decrease was present in bilateral anterior parietal cortex ( P < 0.01 voxel-level; P < 0.05 volume corrected). Activation changes after TMS of left superior parietal cortex thus appears to increase prefrontal and posterior parietal cortex activation, associated with a reduced function of the anterior parietal cortex, including S2. These changes are thought to reflect an impaired ability to estimate the proprioceptive consequences of movement during its preparation, which is compensated by the increased contribution of more remote parietal and prefrontal cortical regions.

Posterior parietal cortex and episodic retrieval: convergent and divergent effects of attention and memory.

Functional neuroimaging studies of humans engaged in retrieval from episodic memory have revealed a surprisingly consistent pattern of retrieval-related activity in lateral posterior parietal cortex (PPC). Given the well-established role of lateral PPC in subserving goal-directed and reflexive attention, it has been hypothesized that PPC activation during retrieval reflects the recruitment of parietal attention mechanisms during remembering. Here, we evaluate this hypothesis by considering the anatomical overlap of retrieval and attention effects in lateral PPC. We begin by briefly reviewing the literature implicating dorsal PPC in goal-directed attention and ventral PPC in reflexive attention. We then discuss the pattern of dorsal and ventral PPC activation during episodic retrieval, and conclude with consideration of the degree of anatomical convergence across the two domains. This assessment revealed that predominantly divergent subregions of lateral PPC are engaged during acts of episodic retrieval and during goal-directed and reflexive attention, suggesting that PPC retrieval effects reflect functionally distinct mechanisms from these forms of attention. Although attention must play a role in aspects of retrieval, the data reviewed here suggest that further investigation into the relationship between processes of attention and memory, as well as alternative accounts of PPC contributions to retrieval, is warranted.

Cortical processing of mechanical hyperalgesia: A MEG study

Mechanical hyperalgesia may develop following tissue inflammation or nerve injury. Basically, peripheral sensitization leads to primary hyperalgesia at the site of injury, whereas secondary hyperalgesia occurs in the surrounding tissue and results from central sensitization. The present study focuses on the cerebral processing of secondary mechanical hyperalgesia. Primary (S1) and secondary (S2) somatosensory cortices and posterior parietal cortex (PPC) are thought to be involved in cerebral processing of noxious mechanical stimuli. However, their response pattern in the presence of mechanical hyperalgesia remains to be elucidated. Therefore, we investigated the cortical processing of secondary mechanical hyperalgesia using magnetoencephalography (MEG). In 12 healthy subjects mechanoinsensitive c-nociceptors were repetitively stimulated using transcutaneously applied high-current electrical stimulation. This procedure resulted in stable areas of secondary mechanical hyperalgesia. Pin-prick stimuli were applied inside and outside the hyperalgesic area. The corresponding cortical activations were detected and quantified using MEG. We found pin-prick-induced sequential activation of contralateral S1, PPC and S2 as well as activation of ipsilateral S2 during both pin-prick hyperalgesia and normal pin-prick pain. During pin-prick hyperalgesia significantly higher activation was detected in contralateral PPC and bilateral S2 but not in S1 compared to normal pin-prick pain. In contrast to PPC, we found a significant correlation between increases of magnetic field strengths within bilateral S2 with the increase of pain ratings during pin-prick hyperalgesia. We conclude that the S2 cortex may be involved for the processing of secondary mechanical hyperalgesia in the human brain. PPC activation may reflect higher attentional processing during mechanical hyperalgesia.

Cognitive Set Reconfiguration Signaled by Macaque Posterior Parietal Neurons

When faced with problems, we can flexibly change our ways of thinking or our point of view. Our cognitive flexibility arises from this ability of shifting cognitive sets. To elucidate how this dynamic process is implemented in the primate brain, single-unit activity was recorded from the posterior parietal cortex (PPC) of two monkeys performing analogs of the Wisconsin Card Sorting Test, which is most commonly used to test cognitive flexibility in humans. We successfully trained the monkeys to promptly perform set shifting, mostly within a single trial, and found shift-related activity: PPC neurons were transiently activated when the monkeys shifted from one cognitive set to another, but not when they shifted in the opposite direction. This shift-related activity emerged about 4 s before the actual behavioral responses, and it well predicted whether the cognitive set would be successfully shifted. These results provide insights into single-unit level mechanisms of cognitive flexibility.

Attentional demands predict short-term memory load response in posterior parietal cortex

Limits to the capacity of visual short-term memory (VSTM) indicate a maximum storage of only 3 or 4 items. Recently, it has been suggested that activity in a specific part of the brain, the posterior parietal cortex (PPC), is correlated with behavioral estimates of VSTM capacity and might reflect a capacity-limited store. In three experiments that varied the delay period and the stimuli to be stored, we found dissociations between functional magnetic resonance imaging (fMRI) activity in PPC and behavioral measures of capacity. When the delay length increased, fMRI activity in this area increased with memory load beyond the behaviorally determined limits of capacity. The results suggest that activity in PPC may reflect the attentional demands of short-term memory rehearsal processes rather than capacity limitations, and imply that a larger number of items than that determined by behavioral measures of capacity may be rehearsed during STM tasks. This account is consistent with the role of PPC in attentional processes and with the close correlation between brain areas that are involved in attention and those that mediate STM.

TMS-Adaptation Reveals Abstract Letter Selectivity in the Left Posterior Parietal Cortex

Activation of the left posterior parietal cortex (PPC) has been associated with the encoding of letters independent of visual form. Here we used transcranial magnetic stimulation (TMS)-adaptation to investigate whether this abstract letter selectivity plays a causal role in letter processing. Visual adaptation was used to manipulate the initial activation state of neurons tuned to different letters prior to the application of TMS, after which subjects performed a detection task on letters that were presented in a different case from the adapting letter. After adaptation, TMS applied over the left PPC facilitated the detection of the adapted letter, whereas it had no impact on the detection of nonadapted letters. TMS applied over the right PPC had no significant effect on either type of letter. This interaction between adaptation and the effects of left PPC TMS demonstrates that adaptation modulated neural activity in the left PPC and thus demonstrates abstract letter selectivity in this region. Importantly, as the adapted letter and the target letters were presented in different cases, this finding demonstrates that the left PPC plays a causal role in letter processing independent of visual form.

Posterior parietal cortex and episodic encoding: Insights from fMRI subsequent memory effects and dual-attention theory

The formation of episodic memories—memories for life events—is affected by attention during event processing. A leading neurobiological model of attention posits two separate yet interacting systems that depend on distinct regions in lateral posterior parietal cortex (PPC). From this dual-attention perspective, dorsal PPC is thought to support the goal-directed allocation of attention, whereas ventral PPC is thought to support reflexive orienting to information that automatically captures attention. To advance understanding of how parietal mechanisms may impact event encoding, we review functional MRI studies that document the relationship between lateral PPC activation during encoding and subsequent memory performance (e.g., later remembering or forgetting). This review reveals that (a) encoding-related activity is frequently observed in human lateral PPC, (b) increased activation in dorsal PPC is associated with later memory success, and (c) increased activation in ventral PPC predominantly correlates with later memory failure. From a dual-attention perspective, these findings suggest that allocating goal-directed attention during event processing increases the probability that the event will be remembered later, whereas the capture of reflexive attention during event processing may have negative consequences for event encoding. The prevalence of encoding-related activation in parietal cortex suggests that neurobiological models of episodic memory should consider how parietal-mediated attentional mechanisms regulate encoding.

Similarity Effect and Optimal Control of Multiple-Choice Decision Making

Decision making with several choice options is central to cognition. To elucidate the neural mechanisms of such decisions, we investigated a recurrent cortical circuit model in which fluctuating spiking neural dynamics underlie trial-by-trial stochastic decisions. The model encodes a continuous analog stimulus feature and is thus applicable to multiple-choice decisions. Importantly, the continuous network captures similarity between alternatives and possible overlaps in their neural representation. Model simulations accounted for behavioral as well as single-unit neurophysiological data from a recent monkey experiment and revealed testable predictions about the patterns of error rate as a function of the similarity between the correct and actual choices. We also found that the similarity and number of options affect speed and accuracy of responses. A mechanism is proposed for flexible control of speed-accuracy tradeoff, based on a simple top-down signal to the decision circuit that may vary nonmonotonically with the number of choice alternatives.

Decoding Trajectories from Posterior Parietal Cortex Ensembles

High-level cognitive signals in the posterior parietal cortex (PPC) have previously been used to decode the intended endpoint of a reach, providing the first evidence that PPC can be used for direct control of a neural prosthesis (Musallam et al., 2004). Here we expand on this work by showing that PPC neural activity can be harnessed to estimate not only the endpoint but also to continuously control the trajectory of an end effector. Specifically, we trained two monkeys to use a joystick to guide a cursor on a computer screen to peripheral target locations while maintaining central ocular fixation. We found that we could accurately reconstruct the trajectory of the cursor using a relatively small ensemble of simultaneously recorded PPC neurons. Using a goal-based Kalman filter that incorporates target information into the state-space, we showed that the decoded estimate of cursor position could be significantly improved. Finally, we tested whether we could decode trajectories during closed-loop brain control sessions, in which the real-time position of the cursor was determined solely by a monkey's neural activity in PPC. The monkey learned to perform brain control trajectories at 80% success rate (for 8 targets) after just 4-5 sessions. This improvement in behavioral performance was accompanied by a corresponding enhancement in neural tuning properties (i.e., increased tuning depth and coverage of encoding parameter space) as well as an increase in off-line decoding performance of the PPC ensemble.

Central processing of tactile and nociceptive stimuli in complex regional pain syndrome

Objective Patients with complex regional pain syndrome (CRPS) suffer from continuous regional limb pain and from hyperesthesia to touch and pain. To better understand the pathophysiological mechanisms underlying the hyperesthesia of CRPS patients, we investigated their cortical processing of touch and acute pain. Methods Cortical responses to tactile stimuli applied to the thumbs, index and little fingers (D1, D2, and D5) and nociceptive stimuli delivered to dorsa of the hands were recorded with a whole-scalp neuromagnetometer from eight chronic CRPS patients and from nine healthy control subjects. Results In the patients, primary somatosensory (SI) cortex activation to tactile stimulation of D2 was significantly stronger, and the D1–D5 distance in SI was significantly smaller for the painful hand compared to the healthy hand. The PPC activation to tactile stimulation was significantly weaker in the patients than in the control subjects. To nociceptive stimulation with equal laser energy, the secondary somatosensory (SII) cortices and posterior parietal cortex (PPC) were similarly activated in both groups. The PPC source strength correlated with the pain rating in the control subjects, but not in the patients. Conclusions The enhanced SI activation in hyperesthetic CRPS patients may reflect central sensitization to touch. The decreased D1–D5 distance implies permanent changes in SI hand representations in chronic CRPS. The defective PPC activation could be associated with the neglect-like symptoms of the patients. As the SII and PPC responses were not enhanced in the CRPS patients, other brain areas are likely to contribute to the observed hyperesthesia to pain. Significance Our results indicate changes of somatosensory processing at cortical level in CRPS.

Evoked magnetic fields following noxious laser stimulation of the thigh in humans

Primary somatosensory cortex (SI) and posterior parietal cortex (PPC) are activated by noxious stimulation. In neurophysiological studies using magnetoencephalography (MEG), however, it has been difficult to separate the activity in SI from that in PPC following stimulation of the upper limb, since the hand area of SI is very close to PPC. Therefore, we investigated human pain processing using MEG following the application of a thulium-YAG laser to the left thigh to separate the activation of SI and PPC, and to clarify the time course of the activities involved. The results indicated that cortical activities were recorded around SI, contralateral secondary somatosensory cortex (cSII), ipsilateral secondary somatosensory cortex (iSII), and PPC between 150–185 ms. The precise location of PPC was indicated to be the inferior parietal lobule (IPL), corresponding to Brodmann's area 40. The mean peak latencies of SI, cSII, iSII and IPL were 152, 170, 181, and 183 ms, respectively. This is the first study to clarify the time course of the activities of SI, SII, and PPC in human pain processing using MEG.