rTMS over the human medial parietal cortex impairs online reaching corrections.

Indirect correlational evidence suggests that the posteromedial sector of the human parietal cortex (area hV6A) is involved in reaching corrections. We interfered with hV6A functions using repetitive transcranial magnetic stimulation (rTMS) while healthy participants performed reaching movements and in-flight adjustments of the hand trajectory in presence of unexpected target shifts. rTMS over hV6A specifically altered action reprogramming, causing deviations of the shifted trajectories, particularly along the vertical dimension (i.e., distance). This study provides evidence of the functional relevance of hV6A in action reprogramming while a sudden event requires a change in performance and shows that hV6A also plays a role in state estimation during reaching. These findings are in line with neurological data showing impairments in actions performed along the distance dimension when lesions occur in the dorsal posterior parietal cortex.

Biases in the spectral amplitude distribution of a natural scene modulate horizontal size perception.

Introduction: Visual perception is a complex process that involves the analysis of different spatial and temporal features of the visual environment. One critical aspect of this process is adaptation, which allows the visual system to adjust its sensitivity to specific features based on the context of the environment. Numerous theories highlight the significance of the visual scene and its spectral properties in perceptual and adaptation mechanisms. For example, size perception is known to be influenced by the spatial frequency content of the visual scene. Nonetheless, several inquiries still exist, including how specific spectral properties of the scene play a role in size perception and adaptation mechanisms. Methods: In this study, we explore aftereffects on size perception following adaptation to a natural scene with a biased spectral amplitude distribution. Twenty participants had to manually estimate the horizontal size of a projected rectangle after adaptation to three visually biased conditions: vertical-biased, non-biased, and horizontal-biased. Size adaptation aftereffects were quantified by comparing the perceptual responses from the non-biased condition with the vertical- and horizontal-biased conditions. Results: We found size perception shifts which were contingent upon the specific orientation and spatial frequency distribution inherent in the amplitude spectra of the adaptation stimuli. Particularly, adaptation to vertical-biased produced a horizontal enlargement, while adaptation to horizontal-biased generated a decrease in the horizontal size perception of the rectangle. On average, size perception was modulated by 5-6%. Discussion: These findings provide supporting evidence for the hypothesis that the neural mechanisms responsible for processing spatial frequency channels are involved in the encoding and perception of size information. The implications for neural mechanisms underlying spatial frequency and size information encoding are discussed.

The influence of action on perception spans different effectors.

Perception and action are fundamental processes that characterize our life and our possibility to modify the world around us. Several pieces of evidence have shown an intimate and reciprocal interaction between perception and action, leading us to believe that these processes rely on a common set of representations. The present review focuses on one particular aspect of this interaction: the influence of action on perception from a motor effector perspective during two phases, action planning and the phase following execution of the action. The movements performed by eyes, hands, and legs have a different impact on object and space perception; studies that use different approaches and paradigms have formed an interesting general picture that demonstrates the existence of an action effect on perception, before as well as after its execution. Although the mechanisms of this effect are still being debated, different studies have demonstrated that most of the time this effect pragmatically shapes and primes perception of relevant features of the object or environment which calls for action; at other times it improves our perception through motor experience and learning. Finally, a future perspective is provided, in which we suggest that these mechanisms can be exploited to increase trust in artificial intelligence systems that are able to interact with humans.

Machine learning methods detect arm movement impairments in a patient with parieto-occipital lesion using only early kinematic information.

Patients with lesions of the parieto-occipital cortex typically misreach visual targets that they correctly perceive (optic ataxia). Although optic ataxia was described more than 30 years ago, distinguishing this condition from physiological behavior using kinematic data is still far from being an achievement. Here, combining kinematic analysis with machine learning methods, we compared the reaching performance of a patient with bilateral occipitoparietal damage with that of 10 healthy controls. They performed visually guided reaches toward targets located at different depths and directions. Using the horizontal, sagittal, and vertical deviation of the trajectories, we extracted classification accuracy in discriminating the reaching performance of patient from that of controls. Specifically, accurate predictions of the patient's deviations were detected after the 20% of the movement execution in all the spatial positions tested. This classification based on initial trajectory decoding was possible for both directional and depth components of the movement, suggesting the possibility of applying this method to characterize pathological motor behavior in wider frameworks.

Severe lactic acidosis and persistent diastolic hypotension following standard dose of intermittent nebulized salbutamol in a child: a case report.

BACKGROUND: Salbutamol is a selective ß2-receptor agonist widely used to treat asthma in both emergency and outpatient settings. However, it has been associated with a broad spectrum of side effects. Lactic acidosis and diastolic hypotension are rarely reported together following intermittent salbutamol nebulization in children, even less so at standard therapeutic doses. CASE PRESENTATION: We present the case of a 12-year-old Italian boy, 34 kg body weight, who experienced a serious drug reaction during a moderate asthma exacerbation with associated dehydration (blood urea nitrogen/creatinine 0.25), following intermittent inhaled (0.2 mg at 3-hour intervals-overall 1.4 mg in 24 hours before arrival) and nebulized treatment (3.25 mg at 20-minute intervals in 60 minutes, overall 11.25 mg in our emergency department). The patient developed hyperglycemia (peak concentration 222 mg/dL), hypokalemia (lowest concentration 2.6 mEq/L), electrocardiogram alterations (corrected QT interval 467 ms), long-lasting arterial hypotension despite fluid boluses (lowest value 87/33 mmHg), and elevated blood lactate levels (peak concentration 8.1 mmol/L), following the third nebulized dose. Infections, liver dysfunction, and toxicity following other medications were ruled out. The aforementioned alterations improved within 24 hours after discontinuation of salbutamol. CONCLUSIONS: We reinforce the message that even the use of intermittent nebulized salbutamol for acute moderate asthma can lead to severe transient complications in children. Then, healthcare providers should pay attention not only in emergency settings, to achieve prompt recognition and proper management of this adverse reaction. Careful reassessment could prevent similar reactions.

A Multifunctional Adaptive and Interactive AI system to support people living with stroke, acquired brain or spinal cord injuries: A study protocol.

BACKGROUND: Acquired brain injury and spinal cord injury are leading causes of severe motor disabilities impacting a person's autonomy and social life. Enhancing neurological recovery driven by neurogenesis and neuronal plasticity could represent future solutions; however, at present, recovery of activities employing assistive technologies integrating artificial intelligence is worthy of examining. MAIA (Multifunctional, adaptive, and interactive AI system for Acting in multiple contexts) is a human-centered AI aiming to allow end-users to control assistive devices naturally and efficiently by using continuous bidirectional exchanges among multiple sensorimotor information. METHODS: Aimed at exploring the acceptability of MAIA, semi-structured interviews (both individual interviews and focus groups) are used to prompt possible end-users (both patients and caregivers) to express their opinions about expected functionalities, outfits, and the services that MAIA should embed, once developed, to fit end-users needs. DISCUSSION: End-user indications are expected to interest MAIA technical, health-related, and setting components. Moreover, psycho-social issues are expected to align with the technology acceptance model. In particular, they are likely to involve intrinsic motivational and extrinsic social aspects, aspects concerning the usefulness of the MAIA system, and the related ease to use. At last, we expect individual factors to impact MAIA: gender, fragility levels, psychological aspects involved in the mental representation of body image, personal endurance, and tolerance toward AT-related burden might be the aspects end-users rise in evaluating the MAIA project.

Horizontal target size perturbations during grasping movements are described by subsequent size perception and saccade amplitude.

Perception and action are essential in our day-to-day interactions with the environment. Despite the dual-stream theory of action and perception, it is now accepted that action and perception processes interact with each other. However, little is known about the impact of unpredicted changes of target size during grasping actions on perception. We assessed whether size perception and saccade amplitude were affected before and after grasping a target that changed its horizontal size during the action execution under the presence or absence of tactile feedback. We have tested twenty-one participants in 4 blocks of 30 trials. Blocks were divided into two experimental tactile feedback paradigms: tactile and non-tactile. Trials consisted of 3 sequential phases: pre-grasping size perception, grasping, and post-grasping size perception. During pre- and post-phases, participants executed a saccade towards a horizontal bar and performed a manual size estimation of the bar size. During grasping phase, participants were asked to execute a saccade towards the bar and to make a grasping action towards the screen. While grasping, 3 horizontal size perturbation conditions were applied: non-perturbation, shortening, and lengthening. 30% of the trials presented perturbation, meaning a symmetrically shortened or lengthened by 33% of the original size. Participants' hand and eye positions were assessed by a motion capture system and a mobile eye-tracker, respectively. After grasping, in both tactile and non-tactile feedback paradigms, size estimation was significantly reduced in lengthening (p = 0.002) and non-perturbation (p<0.001), whereas shortening did not induce significant adjustments (p = 0.86). After grasping, saccade amplitude became significantly longer in shortening (p<0.001) and significantly shorter in lengthening (p<0.001). Non-perturbation condition did not display adjustments (p = 0.95). Tactile feedback did not generate changes in the collected perceptual responses, but horizontal size perturbations did so, suggesting that all relevant target information used in the movement can be extracted from the post-action target perception.

Multiple, random spot urine sampling for estimating urinary sodium excretion.

The measurement of sodium intake may be important for the management of hypertension. Dietary surveys and 24-h urinary collection are often unreliable and/or impractical. We hypothesized that urinary sodium excretion can be accurately estimated through multiple spot urine samples from different days. All enrolled subjects were children of the coauthors of the study. Fifty-two 24-h urinary collections (4 per subject) for measuring sodium excretion and the 297 related urinary samples (1 per voiding) were collected for calculating the urinary sodium/urinary creatinine ratio in 13 children. The mean of 4 measured sodium excretions served as the individual "gold standard". Twenty-four urinary collections were used to generate the equation predicting the mean measured sodium excretion from the mean of 4 urinary sodium/urinary creatinine [= 0.016 × urinary sodium (mmol/L) / urinary creatinine (mmol/L) ratio + 3.3)]; the remaining 28 urinary collections and 153 urinary samples were used for the external validation. All subjects underwent an additional validation procedure involving 12 urinary samples randomly collected on different days 6 months apart. The performance of sodium excretion calculated from a total of over 22,000 possible means of 4 out of all the available urinary samples, randomly taken on different days, was analyzed as to precision (by means of the coefficient of variation) and as to accuracy (by means of the P30). The coefficients of variations of measured vs. calculated sodium excretion were 25.3% vs. 25.8%, and the P30 of calculated sodium excretion was 100%. The excellent performance of calculated sodium excretion was confirmed both by external validation and by samples collected 6 months apart with mean P30s, all between 86 and 100%.Conclusion: In the described experimental conditions, urinary sodium excretion was estimated with equal precision and more accurately (and practically) by the mean of 4 urinary sodium/urinary creatinine ratios from random samples from different days than by a single urinary collection. In real life, with several errors systematically affecting urinary collection, the superiority of calculated sodium excretion is likely to be even greater. What is Known: • The measurement of sodium intake with the current standards of care (dietary survey or 24-h urinary collection) is laborious and can be inaccurate. What is New: • The study provides evidence that sodium intake can be estimated equally precisely, more accurately and more practically with the urinary sodium-to-urinary creatinine ratio from 4 urine samples taken on different days than with a single urinary collection.

Transcranial Magnetic Stimulation Over the Human Medial Posterior Parietal Cortex Disrupts Depth Encoding During Reach Planning.

Accumulating evidence supports the view that the medial part of the posterior parietal cortex (mPPC) is involved in the planning of reaching, but while plenty of studies investigated reaching performed toward different directions, only a few studied different depths. Here, we investigated the causal role of mPPC (putatively, human area V6A-hV6A) in encoding depth and direction of reaching. Specifically, we applied single-pulse transcranial magnetic stimulation (TMS) over the left hV6A at different time points while 15 participants were planning immediate, visually guided reaching by using different eye-hand configurations. We found that TMS delivered over hV6A 200 ms after the Go signal affected the encoding of the depth of reaching by decreasing the accuracy of movements toward targets located farther with respect to the gazed position, but only when they were also far from the body. The effectiveness of both retinotopic (farther with respect to the gaze) and spatial position (far from the body) is in agreement with the presence in the monkey V6A of neurons employing either retinotopic, spatial, or mixed reference frames during reach plan. This work provides the first causal evidence of the critical role of hV6A in the planning of visually guided reaching movements in depth.

Distress in Infants and Young Children: Don't Blame Acid Reflux.

OBJECTIVE: The role of gastroesophageal reflux (GER) causing distress in infants is controversial but acid inhibitors are often empirically prescribed. We evaluated the relation between distress assessed by the Face, Legs, Activity, Cry, Consolability (FLACC) scale and GER in infants. METHODS: We analyzed multiple intraluminal impedance-pH (MII-pH) monitoring tracings of infants with persistent unexplained fussiness or distress. Symptoms occurring during investigation were scored by parents using the FLACC scale and were grouped as "distress" episodes. RESULTS: We recruited 62 children (ages 15 days to 23 months, median age 3.5 months). During MII-pH, 452 episodes of distress were registered: 217 (48%) were temporally associated with GER and 235 (52%) were not, with no difference in the median value of FLACC between the 2 groups. Infants with abnormal acid exposure index had a significantly lower FLACC compared with the group with acid reflux index <7% (P < 0.001). When associated with symptoms, GER occurred significantly more often before than simultaneously or after an episode of distress (P = 0.001). Age, proximal extension, and duration of GER did not correlate with FLACC scores. Episodes of distress associated with nonacid reflux presented a significant higher FLACC compared with the ones with acid content (FLACC 6 vs 5, P = 0.011). In infants, episodes of distress do not significantly correlate with GER. CONCLUSIONS: No difference in infant distress was noted between proximal and distal GER. Non-acid reflux is perceived at least as painful than acid GER. Our results stress that acid inhibitors should not be started in infants presenting distress unless a clear association with acid GER is demonstrated.

Trans-saccadic adaptation of perceived size independent of saccadic adaptation.

Systematic shortening or lengthening of target objects during saccades modifies saccade amplitudes and perceived size of the objects. These two events are concomitant when size change during the saccade occurs asymmetrically, thereby shifting the center of mass of the object. In the present study, we asked whether or not the two are necessarily linked. We tested human participants in symmetrical systematic shortening and lengthening of a vertical bar during a horizontal saccade, aiming to not modify the saccade amplitude. Before and after a phase of trans-saccadic changes of the target bar, participants manually indicated the sizes of various vertically oriented bars by open-loop grip aperture. We evaluated the effect of trans-saccadic changes of bar length on manual perceptual reports and whether this change depended on saccade amplitude. As expected, we did not induce any change in horizontal or vertical components of saccade amplitude, but we found a significant difference in perceived size after the lengthening experiment compared to after the shortening experiment. Moreover, after the lengthening experiment, perceived size differed significantly from pre-lengthening baseline. These findings suggest that a change of size perception can be induced trans-saccadically, and its mechanism does not depend on saccadic amplitude change.

Neurons Modulated by Action Execution and Observation in the Macaque Medial Parietal Cortex.

The observation of an action evokes discharges in a rich network of cortical areas [1-14]. In the present study, we have evaluated the effect of grasp execution and of the observation of others' grasping on the activity of neurons in the medial parietal area V6A, an area of the reach-to-grasp network never explored to date in this regard. Although V6A neurons are typically active during one's own grasping execution but not while one observes another's grasping, a minority of neurons showed mirror properties, active both when monkeys performed the task and when they observed it being performed by the experimenter. Recent studies have shown that the discharge of mirror neurons may vary from congruent to noncongruent [7, 10, 15-17], but most mirror neurons show a clear relation between the visual action they respond to and the motor response they code [10], thus matching the sensory description of an observed action with its corresponding internal motor representation. In all V6A putative mirror neurons, instead, neural representations during execution and observation were highly dissimilar, discounting the possibility that V6A specifically encodes the grip type performed by another agent. Notably, we have found that in these neurons, the neural representation of an object changed according to whether grasping was allowed or performed and whether the object was the target of another agent's grasping. In other words, rather than code another agent's observed action, V6A neurons appear to primarily encode the relevance, in the grasping context, of the target object.

Brief resolved unexplained events: Retrospective validation of diagnostic criteria and risk stratification.

BACKGROUND AND OBJECTIVES: This study retrospectively evaluated the AAP guidelines for diagnosis and risk stratification of Brief Resolved Unexplained Events (BRUE) in a well-characterized cohort of infants admitted with an Apparent Life Threatening Event (ALTE). Further, using prospective follow-up, we endeavored to determine the safety of implementing ambulatory care for the lower risk BRUE population (LR-BRUE) and estimate the cost-savings of this practice. METHODS: Retrospective application of the BRUE criteria on infants younger than 12 months of age who had been admitted with an ALTE from 2006 to 2016 at a single tertiary care center in Lombardy, Italy. ALTE patients were classified into three groups; (1) Not a BRUE; (2) Lower-risk (LR)-BRUE; and (3) Higher-risk (HR)-BRUE. Patients were contacted prospectively to obtain long-term follow-up outcomes and medical records and billing databases were reviewed. RESULTS: Among the 84 infants admitted for an ALTE, 35 (42%) were not a BRUE, 16 (19%) were a LR-BRUE, and 33 (39%) were a HR-BRUE. Only one of the LR-BRUE patients had a subsequent LR-BRUE event, and was later diagnosed with a seizure disorder. Two HR-BRUE babies had also previously presented with a LR-BRUE. Application of the LR-BRUE guidelines would have decreased health expenditure by 20%. There were no deaths or significant morbidities in either BRUE group. CONCLUSIONS: Applying the recent AAP BRUE guidelines and risk stratification to a well-characterized cohort of admitted ALTE patients is a safe and cost-effective approach. Careful out-patient follow-up is recommended as one of our patients with a LR-BRUE had a recurrence, and was subsequently diagnosed with a seizure disorder.

Preparatory activity for purposeful arm movements in the dorsomedial parietal area V6A: Beyond the online guidance of movement.

Over the years, electrophysiological recordings in macaque monkeys performing visuomotor tasks brought about accumulating evidence for the expression of neuronal properties (e.g., selectivity in the visuospatial and somatosensory domains, encoding of visual affordances and motor cues) in the posterior parietal area V6A that characterize it as an ideal neural substrate for online control of prehension. Interestingly, neuroimaging studies suggested a role of putative human V6A also in action preparation; moreover, pre-movement population activity in monkey V6A has been recently shown to convey grip-related information for upcoming grasping. Here we directly test whether macaque V6A neurons encode preparatory signals that effectively differentiate between dissimilar actions before movement. We recorded the activity of single V6A neurons during execution of two visuomotor tasks requiring either reach-to-press or reach-to-grasp movements in different background conditions, and described the nature and temporal dynamics of V6A activity preceding movement execution. We found striking consistency in neural discharges measured during pre-movement and movement epochs, suggesting that the former is a preparatory activity exquisitely linked to the subsequent execution of particular motor actions. These findings strongly support a role of V6A beyond the online guidance of movement, with preparatory activity implementing suitable motor programs that subsequently support action execution.

Prediction of Reach Goals in Depth and Direction from the Parietal Cortex.

The posterior parietal cortex is well known to mediate sensorimotor transformations during the generation of movement plans, but its ability to control prosthetic limbs in 3D environments has not yet been fully demonstrated. With this aim, we trained monkeys to perform reaches to targets located at various depths and directions and tested whether the reach goal position can be extracted from parietal signals. The reach goal location was reliably decoded with accuracy close to optimal (>90%), and this occurred also well before movement onset. These results, together with recent work showing a reliable decoding of hand grip in the same area, suggest that this is a suitable site to decode the entire prehension action, to be considered in the development of brain-computer interfaces.

Interplay Between Grip and Vision in the Monkey Medial Parietal Lobe.

We aimed at understanding the relative contribution of visual information and hand shaping to the neuronal activity of medial posterior parietal area V6A, a newly added area in the monkey cortical grasping circuit. Two Macaca fascicularis performed a Reach-to-Grasp task in the dark and in the light, grasping objects of different shapes. We found that V6A contains Visual cells, activated only during grasping in the light; Motor neurons, equally activated during grasping in the dark and in the light; Visuomotor cells, differently activated while grasping in the dark and in the light. Visual, Motor, and Visuomotor neurons were moderately or highly selective during grasping, whereas they reduced their selectivity during object observation without performing grasping. The use of the same experimental design employed in the dorsolateral grasping area AIP by other authors allowed us to compare the grasp-related properties of V6A and AIP. From these data and from the literature a frame emerges with many similarities between medial grasping area V6A and lateral grasping area AIP: both areas update and control prehension, with V6A less sensitive than AIP to fine visual details of the objects to be grasped, but more involved in coordinating reaching and grasping.

Reaching and grasping actions and their context shape the perception of object size.

Humans frequently estimate the size of objects to grasp them. In fact, when performing an action, our perception is focused towards the visual properties of the object that enable us to successfully execute the action. However, the motor system is also able to influence perception, but only a few studies have reported evidence for action-induced visual perception modifications. Here, we aimed to look for a feature-specific perceptual modulation before and after a reaching or a grasping action. Human participants were instructed to either reach for or grasp two-dimensional bars of different size and to perform a size perceptual task before and after the action in two contexts: in one where they knew the subsequent type of movement and in the other where they did not know. We found significant modifications of perceived size of stimuli more pronounced after grasping than after reaching. The mere knowledge of the subsequent action type significantly affected the size perception before the movement execution, with consistent results in both manual and verbal reports. These data represent direct evidence that, in natural conditions without manipulation of visual information, the action type and the action context dynamically modulate size perception, by shaping it according to relevant information required to recognize and interact with objects.

Multiple Coordinate Systems and Motor Strategies for Reaching Movements When Eye and Hand Are Dissociated in Depth and Direction.

Reaching behavior represents one of the basic aspects of human cognitive abilities important for the interaction with the environment. Reaching movements towards visual objects are controlled by mechanisms based on coordinate systems that transform the spatial information of target location into appropriate motor response. Although recent works have extensively studied the encoding of target position for reaching in three-dimensional space at behavioral level, the combined analysis of reach errors and movement variability has so far been investigated by few studies. Here we did so by testing 12 healthy participants in an experiment where reaching targets were presented at different depths and directions in foveal and peripheral viewing conditions. Each participant executed a memory-guided task in which he/she had to reach the memorized position of the target. A combination of vector and gradient analysis, novel for behavioral data, was applied to analyze patterns of reach errors for different combinations of eye/target positions. The results showed reach error patterns based on both eye- and space-centered coordinate systems: in depth more biased towards a space-centered representation and in direction mixed between space- and eye-centered representation. We calculated movement variability to describe different trajectory strategies adopted by participants while reaching to the different eye/target configurations tested. In direction, the distribution of variability between configurations that shared the same eye/target relative configuration was different, whereas in configurations that shared the same spatial position of targets, it was similar. In depth, the variability showed more similar distributions in both pairs of eye/target configurations tested. These results suggest that reaching movements executed in geometries that require hand and eye dissociations in direction and depth showed multiple coordinate systems and different trajectory strategies according to eye/target configurations and the two dimensions of space.

Decoding Information for Grasping from the Macaque Dorsomedial Visual Stream.

Neurodecoders have been developed by researchers mostly to control neuroprosthetic devices, but also to shed new light on neural functions. In this study, we show that signals representing grip configurations can be reliably decoded from neural data acquired from area V6A of the monkey medial posterior parietal cortex. Two Macaca fascicularis monkeys were trained to perform an instructed-delay reach-to-grasp task in the dark and in the light toward objects of different shapes. Population neural activity was extracted at various time intervals on vision of the objects, the delay before movement, and grasp execution. This activity was used to train and validate a Bayes classifier used for decoding objects and grip types. Recognition rates were well over chance level for all the epochs analyzed in this study. Furthermore, we detected slightly different decoding accuracies, depending on the task's visual condition. Generalization analysis was performed by training and testing the system during different time intervals. This analysis demonstrated that a change of code occurred during the course of the task. Our classifier was able to discriminate grasp types fairly well in advance with respect to grasping onset. This feature might be important when the timing is critical to send signals to external devices before the movement start. Our results suggest that the neural signals from the dorsomedial visual pathway can be a good substrate to feed neural prostheses for prehensile actions.SIGNIFICANCE STATEMENT Recordings of neural activity from nonhuman primate frontal and parietal cortex have led to the development of methods of decoding movement information to restore coordinated arm actions in paralyzed human beings. Our results show that the signals measured from the monkey medial posterior parietal cortex are valid for correctly decoding information relevant for grasping. Together with previous studies on decoding reach trajectories from the medial posterior parietal cortex, this highlights the medial parietal cortex as a target site for transforming neural activity into control signals to command prostheses to allow human patients to dexterously perform grasping actions.

Vision for Prehension in the Medial Parietal Cortex.

In the last 2 decades, the medial posterior parietal area V6A has been extensively studied in awake macaque monkeys for visual and somatosensory properties and for its involvement in encoding of spatial parameters for reaching, including arm movement direction and amplitude. This area also contains populations of neurons sensitive to grasping movements, such as wrist orientation and grip formation. Recent work has shown that V6A neurons also encode the shape of graspable objects and their affordance. In other words, V6A seems to encode object visual properties specifically for the purpose of action, in a dynamic sequence of visuomotor transformations that evolve in the course of reach-to-grasp action.We propose a model of cortical circuitry controlling reach-to-grasp actions, in which V6A acts as a comparator that monitors differences between current and desired hand positions and configurations. This error signal could be used to continuously update the motor output, and to correct reach direction, hand orientation, and/or grip aperture as required during the act of prehension.In contrast to the generally accepted view that the dorsomedial component of the dorsal visual stream encodes reaching, but not grasping, the functional properties of V6A neurons strongly suggest the view that this area is involved in encoding all phases of prehension, including grasping.