The role of the caudal superior parietal lobule in updating hand location in peripheral vision: further evidence from optic ataxia

Comparison of cortical gyrification patterns in patients with panic disorder with and without comorbid generalized anxiety disorder

BACKGROUND

Lower functioning and higher symptom severity are observed when panic disorder (PD) co-occurs with generalized anxiety disorder (PD + GAD). No research on cortical gyrification patterns in the PD + GAD group has been conducted to date, which could show the alterations in brain connectivity in the extended fear network (EFN). This study aimed to investigate the characteristics of cortical gyrification in the PD + GAD group, compared to that in the PD without comorbid GAD (PD-GAD) group.

METHODS

This study included 90 patients with PD, with propensity score matching between the PD + GAD (n = 30) and PD-GAD groups (n = 60), and 65 healthy controls (HC). For clinical evaluation, we assessed the anxiety symptomatology, suicidality, and harm avoidance. The local gyrification index (LGI) was obtained from T1-weighted brain MRI data using FreeSurfer.

RESULTS

In the PD group compared to the HC, the hypergyrification involved the EFN. In the PD + GAD group compared to the PD-GAD group, hypergyrification was shown in the pathological worry-related brain regions. Within the PD + GAD group, significant positive correlations were observed between the superior frontal gyrus LGI values and suicidality scores, as well as between the superior parietal gyrus LGI values and harm avoidance levels.

LIMITATIONS

Given the variability in cortical gyrification patterns, longitudinal studies are needed to assess the occurrence of hypergyrification in specific brain regions.

CONCLUSIONS

This study is the first to demonstrate cortical gyrification patterns in the PD + GAD group compared to those in the PD-GAD group. Notably, the EFN and pathological worry-related brain regions have been implicated in the pathology of PD + GAD.

Investigating the Link Between Subjective Depth Perception Deficits and Objective Stereoscopic Vision Deficits in Individuals With Acquired Brain Injury

Individuals with acquired brain injury have reported subjective complaints of depth perception deficits, but few have undergone objective assessments to confirm these deficits. As a result, the literature currently lacks reports detailing the correlation between subjective depth perception deficits and objective stereoscopic vision deficits in individuals with acquired brain injury, particularly those cases that are characterized by a clearly defined lesion. To investigate this relationship, we recruited three individuals with acquired brain injury who experienced depth perception deficits and related difficulties in their daily lives. We had them take neurologic, ophthalmological, and neuropsychological examinations. We also had them take two types of stereoscopic vision tests: a Howard-Dolman-type stereoscopic vision test and the Topcon New Objective Stereo Test. Then, we compared the results with those of two control groups: a group with damage to the right hemisphere of the brain and a group of healthy controls. Performance on the two stereoscopic vision tests was severely impaired in the three patients. One of the patients also presented with cerebral diplopia. We identified the potential neural basis of these deficits in the cuneus and the posterior section of the superior parietal lobule, which play a role in vergence fusion and are located in the caudal region of the dorso-dorsal visual pathway, which is known to be crucial not only for visual spatial perception, but also for reaching, grasping, and making hand postures in the further course of that pathway.

Cortical and cerebellar structural correlates of cognitive-motor integration performance in females with and without persistent concussion symptoms

INTRODUCTION

Fifteen percent of individuals who sustain a concussion develop persistent concussion symptoms (PCS). Recent literature has demonstrated atrophy of the frontal, parietal, and cerebellar regions following acute concussive injury. The frontoparietal-cerebellar network is essential for the performance of visuomotor transformation tasks requiring cognitive-motor integration (CMI), important for daily function.

PURPOSE

We investigated cortical and subcortical structural differences and how these differences are associated with CMI performance in those with PCS versus healthy controls.

METHODS

Twenty-six age-matched  female participants (13 PCS, 13 healthy) completed four visuomotor tasks.  Additionally, MR-images were analyzed for cortical thickness and volume, and cerebellar lobule volume.

RESULTS

No statistically significant group differences were found in CMI performance. However, those with PCS demonstrated a significantly thicker and larger precuneus, and significantly smaller cerebellar lobules (VIIIa, VIIIb, X) compared to controls. When groups were combined, volumes of both the cerebellar lobules and cortical regions were associated with CMI task performance.

CONCLUSION

The lack of behavioral differences combined with the structural differences may reflect a compensatory mechanism for those with PCS. In addition, this study highlights the effectiveness of CMI tasks in estimating the structural integrity of the frontoparietal-cerebellar network and is among the first to demonstrate structural correlates of PCS.

A narrative review of the anatomy and function of the white matter tracts in language production and comprehension

Much is known about the role of cortical areas in language processing. The shift towards network approaches in recent years has highlighted the importance of uncovering the role of white matter in connecting these areas. However, despite a large body of research, many of these tracts' functions are not well-understood. We present a comprehensive review of the empirical evidence on the role of eight major tracts that are hypothesized to be involved in language processing (inferior longitudinal fasciculus, inferior fronto-occipital fasciculus, uncinate fasciculus, extreme capsule, middle longitudinal fasciculus, superior longitudinal fasciculus, arcuate fasciculus, and frontal aslant tract). For each tract, we hypothesize its role based on the function of the cortical regions it connects. We then evaluate these hypotheses with data from three sources: studies in neurotypical individuals, neuropsychological data, and intraoperative stimulation studies. Finally, we summarize the conclusions supported by the data and highlight the areas needing further investigation.

Bálint syndrome

This chapter starts by reviewing the various interpretations of Bálint syndrome over time. We then develop a novel integrative view in which we propose that the various symptoms, historically reported and labeled by various authors, result from a core mislocalization deficit. This idea is in accordance with our previous proposal that the core deficit of Bálint syndrome is attentional (Pisella et al., 2009, 2013, 2017) since covert attention improves spatial resolution in visual periphery (Yeshurun and Carrasco, 1998); a deficit of covert attention would thus increase spatial uncertainty and thereby impair both visual object identification and visuomotor accuracy. In peripheral vision, we perceive the intrinsic characteristics of the perceptual elements surrounding us, but not their precise localization (Rosenholtz et al., 2012a,b), such that without covert attention we cannot organize them to their respective and recognizable objects; this explains why perceptual symptoms (simultanagnosia, neglect) could result from visual mislocalization. The visuomotor symptoms (optic ataxia) can be accounted for by both visual and proprioceptive mislocalizations in an oculocentric reference frame, leading to field and hand effects, respectively. This new pathophysiological account is presented along with a model of posterior parietal cortex organization in which the superior part is devoted to covert attention, while the right inferior part is involved in visual remapping. When the right inferior parietal cortex is damaged, additional representational mislocalizations across saccades worsen the clinical picture of peripheral mislocalizations due to an impairment of covert attention.

The posterior parietal cortex processes visuo-spatial and extra-retinal information for saccadic remapping: A case study

Optimally collecting information and controlling behaviour require that we constantly scan our visual environment through eye movements. How the dynamic interaction between short-lived retinal images and extra-retinal signals of eye motion results in our subjective experience of visual stability remains a major issue in Cognitive Neuroscience. The present study aimed to assess and determine the nature of the contribution of the posterior parietal cortex (PPC) to the saccadic remapping mechanisms which contribute to such perceptual visual constancy. Perceptual responses in transsaccadic visual localization tasks were measured in a patient presenting with a PPC lesion and manifesting optic ataxia in the left hemifield with no neglect. Two perceptual localization tasks, each with versus without an intervening saccade, were used: the saccadic suppression of displacement (SSD) task (Ostendorf, Liebermann, & Ploner, 2010) and the peri-saccadic flash localization (LOC) task (Zimmerman & Lappe, 2010). Compared to a group of age-matched healthy subjects, the patient showed a specific pattern of perceptual deficits in the ataxic (left) hemifield. First, a significant impairment occurred in the stationary eye conditions, attesting for an alteration of visuo-spatial encoding. Second, in the saccade conditions, an additional perceptual deficit (an error of ~5° along the saccade direction) was observed in both tasks and mainly in conditions where extra-retinal signals are thought to be critically involved, revealing a constant underestimation by extra-retinal signals of the saccade size, despite preserved saccade accuracy. These findings highlight a crucial role of the PPC in saccadic remapping processes underlying perceptual visual constancy and provide empirical evidence for models such as Ziesche and Hamker's (2014).

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.

Sluggish cognitive tempo and processing speed in adolescents with ADHD: do findings vary based on informant and task?

Few studies have examined whether behavioral sluggish cognitive tempo (SCT) symptoms are related to speeded task performance. Mixed findings in existing research could be due to previous studies using a broad conceptualization of processing speed, not including self-report of SCT symptoms, and relying on non-optimal measures of SCT. Using a multi-informant design with both parent- and adolescent-reported SCT symptoms, the present study provides a preliminary test of the hypothesis that SCT symptoms would be associated with slower performance on tasks having greater graphomotor and fine motor demands. Participants were 80 adolescents (ages 13-17 years; 71% male) with attention-deficit/hyperactivity disorder (ADHD). Adolescents and parents completed ratings of SCT. Adolescents were administered the Wechsler Symbol Search and Coding subtests and the Grooved Pegboard Test. When adjusting for age, sex, and ADHD symptom severity, parent-reported SCT symptoms were not significantly associated with Symbol Search or Coding scores but were significantly associated with slower Grooved Pegboard time. Adolescent-reported SCT symptoms were not significantly associated with Symbol Search but were significantly associated with lower Coding scores and slower Grooved Pegboard time. Findings provide preliminary support for the hypothesis that SCT may be more clearly associated with processing speed task performance as motor demands increase and provide a potential explanation for the mixed literature on SCT in relation to processing speed by demonstrating that the presence and magnitude of associations vary by informant and task.

The Effects of Mild Traumatic Brain Injury on Cognitive-Motor Integration for Skilled Performance

Adults exposed to blast and blunt impact often experience mild traumatic brain injury, affecting neural functions related to sensory, cognitive, and motor function. In this perspective article, we will review the effects of impact and blast exposure on functional performance that requires the integration of these sensory, cognitive, and motor control systems. We describe cognitive-motor integration and how it relates to successfully navigating skilled activities crucial for work, duty, sport, and even daily life. We review our research on the behavioral effects of traumatic impact and blast exposure on cognitive-motor integration in both younger and older adults, and the neural networks that are involved in these types of skills. Overall, we have observed impairments in rule-based skilled performance as a function of both physical impact and blast exposure. The extent of these impairments depended on the age at injury and the sex of the individual. It appears, however, that cognitive-motor integration deficits can be mitigated by the level of skill expertise of the affected individual, suggesting that such experience imparts resiliency in the brain networks that underly the control of complex visuomotor performance. Finally, we discuss the next steps needed to comprehensively understand the impact of trauma and blast exposure on functional movement control.

Optic ataxia: beyond the dorsal stream cliché

This chapter reviews clinical and scientific approaches to optic ataxia. This double historic track allows us to address important issues such as the link between Bálint syndrome and optic ataxia, the alleged double dissociation between optic ataxia and visual agnosia, and the use of optic ataxia to argue for a specific vision-for-action occipitoposterior parietal stream. Clinical cases are described and reveal that perceptual deficits have been long shown to accompany ataxia. Importantly, the term ataxia appears to be misleading as patients exhibit a combination of visual and nonvisual perceptual, attentional, and visuomotor guidance deficits, which are confirmed by experimental approaches. Three major features of optic ataxia are described. The first is a spatial feature whereby the deficits exhibited by patients appear to be specific to peripheral vision, akin to the field effect. Visuomotor field examination allows us to quantify this deficit and reveals that it consists of a highly reliable retinocentric hypometria. The third is a temporal feature whereby these deficits are exacerbated under temporal constraints, i.e., when attending to dynamic stimuli. These two aspects combine in a situation where patients have to quickly respond to a target presented in peripheral vision that is experimentally displaced upon movement onset. In addition to the field effect, a hand effect can be described in conditions where the hand is not visible. Spatial and temporal aspects as well as field and hand effects may rely on several posterior parietal modules that remain to be precisely identified both anatomically and functionally. It is concluded that optic ataxia is not a visuomotor deficit and there is no dissociation between perception and action capacities in optic ataxia, hence a fortiori no double dissociation between optic ataxia and visual agnosia. Future directions for understanding the basic pathophysiology of optic ataxia are proposed.

Robotic exoskeleton assessment of transient ischemic attack

We used a robotic exoskeleton to quantify specific patterns of abnormal upper limb motor behaviour in people who have had transient ischemic attack (TIA). A cohort of people with TIA was recruited within two weeks of symptom onset. All individuals completed a robotic-based assessment of 8 behavioural tasks related to upper limb motor and proprioceptive function, as well as cognitive function. Robotic task performance was compared to a large cohort of controls without neurological impairments corrected for the influence of age. Impairment in people with TIA was defined as performance below the 5^th percentile of controls. Participants with TIA were also assessed with the National Institutes of Health Stroke Scale (NIHSS) score, Chedoke-McMaster Stroke Assessment (CMSA) of the arm, the Behavioural Inattention Test (BIT), the Purdue pegboard test (PPB), and the Montreal Cognitive Assessment (MoCA). Age-related white matter change (ARWMC), prior infarction and cella-media index (CMI) were assessed from baseline CT scan that was performed within 24 hours of TIA. Acute infarction was assessed from diffusion-weighted imaging in a subset of people with TIA. Twenty-two people with TIA were assessed. Robotic assessment showed impaired upper limb motor function in 7/22 people with TIA patients and upper limb sensory impairment in 4/22 individuals. Cognitive tasks involving robotic assessment of the upper limb were completed in 13 participants, of whom 8 (61.5%) showed significant impairment. Abnormal performance in the CMSA arm inventory was present in 12/22 (54.5%) participants. ARWMC was 11.8 ± 6.4 and CMI was 5.4 ± 1.5. DWI was positive in 0 participants. Quantitative robotic assessment showed that people who have had a TIA display a spectrum of upper limb motor and sensory performance deficits as well as cognitive function deficits despite resolution of symptoms and no evidence of tissue infarction.

Reduced regional cerebral blood flow in patients with heart failure

AIMS

Heart failure (HF) patients show significant lateralized neural injury, accompanied by autonomic, mood and cognitive deficits. Both gray and white matter damage occurs and probably develops from altered cerebral blood flow (CBF), a consequence of impaired cardiac output. However, the distribution of regional CBF changes in HF patients is unknown, but is an issue in determining mechanisms of neural injury. Our aim was to compare regional CBF changes in HF with CBF in control subjects using non-invasive pseudo-continuous arterial spin labelling (ASL) procedures.

METHODS AND RESULTS

We collected pseudo-continuous ASL data from 19 HF patients [mean age 55.5 ± 9.1 years; mean body mass index 27.7 ± 5.3 kg/m² ; 13 male) and 29 control subjects (mean age 51.4 ± 5.3 years; mean body mass index 25.7 ± 3.6 kg/m² ; 18 male), using a 3.0-Tesla magnetic resonance imaging (MRI) scanner. Whole-brain CBF maps were calculated, normalized to a common space, smoothed and compared between groups using ANCOVA (covariates; age, gender and gray matter volume). Reduced CBF appeared in multiple sites in HF patients in comparison with controls, with principally lateralized lower flow in temporal, parietal and occipital regions. Areas with decreased CBF included the bilateral prefrontal, frontal, temporal and occipital cortex, thalamus, cerebellum, corona radiate, corpus callosum, hippocampus and amygdala.

CONCLUSIONS

Heart failure patients showed lower, and largely lateralized, CBF in multiple autonomic, mood and cognitive regulatory sites. The reduced CBF is likely to contribute to the lateralized brain injury, leading to the autonomic and neuropsychological deficits found in the condition.

Reachability judgement in optic ataxia: Effect of peripheral vision on hand and target perception in depth

The concept of peripersonal space was first proposed by Rizzolatti, Scandolara, Matelli, and Gentilucci (1981), who introduced the term to highlight the close links between somatosensory and visual processing for stimuli close to the body and suggested that this near-body space could in fact be characterized as an action space (Rizzolatti, Fadiga, Fogassi, & Gallese, 1997). Supporting this idea, patients with right hemisphere lesions have been described as impaired in performing actions towards objects and in perceiving their location - but only when the objects were presented within arm's reach (Bartolo, Carlier, Hassaini, Martin, & Coello, 2014; Brain, 1941). Whether the deficit of optic ataxia patients in processing target locations for action has an effect on the representation of peripersonal space has never been explored. The present study highlights optic ataxia patients' specific difficulties in processing hand-to-target distances in a motor task and in a perceptual task requiring identification of what is reachable in the visual environment. The difficulties are especially evident when both the target and the hand are perceived in the visual periphery. Indeed, when patient I.G. was able to fixate the target, her reaching accuracy and her perception of reachable space both largely improved. Furthermore, the difficulties were enhanced when the hand and the target were both in the lower visual field (in a fixed-far condition vs a fixed-near condition). This novel up-down dimension of optic ataxia fits with the larger representation of the lower visual field in the posterior parietal cortex (Pitzalis et al., 2013; Previc, 1990).

The Contribution of Different Cortical Regions to the Control of Spatially Decoupled Eye-Hand Coordination

Our brain's ability to flexibly control the communication between the eyes and the hand allows for our successful interaction with the objects located within our environment. This flexibility has been observed in the pattern of neural responses within key regions of the frontoparietal reach network. More specifically, our group has shown how single-unit and oscillatory activity within the dorsal premotor cortex (PMd) and the superior parietal lobule (SPL) change contingent on the level of visuomotor compatibility between the eyes and hand. Reaches that involve a coupling between the eyes and hand toward a common spatial target display a pattern of neural responses that differ from reaches that require eye-hand decoupling. Although previous work examined the altered spiking and oscillatory activity that occurs during different types of eye-hand compatibilities, they did not address how each of these measures of neurological activity interacts with one another. Thus, in an effort to fully characterize the relationship between oscillatory and single-unit activity during different types of eye-hand coordination, we measured the spike-field coherence (SFC) within regions of macaque SPL and PMd. We observed stronger SFC within PMdr and superficial regions of SPL (areas 5/PEc) during decoupled reaches, whereas PMdc and regions within SPL surrounding medial intrapareital sulcus had stronger SFC during coupled reaches. These results were supported by meta-analysis on human fMRI data. Our results support the proposal of altered cortical control during complex eye-hand coordination and highlight the necessity to account for the different eye-hand compatibilities in motor control research.

Eye-Hand Coordination during Visuomotor Adaptation with Different Rotation Angles: Effects of Terminal Visual Feedback

This study examined adaptive changes of eye-hand coordination during a visuomotor rotation task under the use of terminal visual feedback. Young adults made reaching movements to targets on a digitizer while looking at targets on a monitor where the rotated feedback (a cursor) of hand movements appeared after each movement. Three rotation angles (30°, 75° and 150°) were examined in three groups in order to vary the task difficulty. The results showed that the 30° group gradually reduced direction errors of reaching with practice and adapted well to the visuomotor rotation. The 75° group made large direction errors of reaching, and the 150° group applied a 180° reversal shift from early practice. The 75°and 150° groups, however, overcompensated the respective rotations at the end of practice. Despite these group differences in adaptive changes of reaching, all groups gradually adapted gaze directions prior to reaching from the target area to the areas related to the final positions of reaching during the course of practice. The adaptive changes of both hand and eye movements in all groups mainly reflected adjustments of movement directions based on explicit knowledge of the applied rotation acquired through practice. Only the 30° group showed small implicit adaptation in both effectors. The results suggest that by adapting gaze directions from the target to the final position of reaching based on explicit knowledge of the visuomotor rotation, the oculomotor system supports the limb-motor system to make precise preplanned adjustments of reaching directions during learning of visuomotor rotation under terminal visual feedback.

The Pointing Errors in Optic Ataxia Reveal the Role of "Peripheral Magnification" of the PPC

Interaction with visual objects in the environment requires an accurate correspondence between visual space and its internal representation within the brain. Many clinical conditions involve some impairment in visuo-motor control and the errors created by the lesion of a specific brain region are neither random nor uninformative. Modern approaches to studying the neuropsychology of action require powerful data-driven analyses and error modeling in order to understand the function of the lesioned areas. In the present paper we carried out mixed-effect analyses of the pointing errors of seven optic ataxia patients and seven control subjects. We found that a small parameter set is sufficient to explain the pointing errors produced by unilateral optic ataxia patients. In particular, the extremely stereotypical errors made when pointing toward the contralesional visual field can be fitted by mathematical models similar to those used to model central magnification in cortical or sub-cortical structure(s). Our interpretation is that visual areas that contain this footprint of central magnification guide pointing movements when the posterior parietal cortex (PPC) is damaged and that the functional role of the PPC is to actively compensate for the under-representation of peripheral vision that accompanies central magnification. Optic ataxia misreaching reveals what would be hand movement accuracy and precision if the human motor system did not include elaborated corrective processes for reaching and grasping to non-foveated targets.

Don't watch where you're going: The neural correlates of decoupling eye and arm movements

"Standard" visually-guided reaching movements consist of a saccade and an arm movement to the same target location. In the current study, functional magnetic resonance imaging was used to contrast brain activity during standard visually-guided reaches with activity during a "non-standard" visuomotor mapping where the targets of the saccade and arm movement were spatially decoupled. Multi-voxel pattern analysis approaches showed discrimination of standard versus non-standard visuomotor mapping in the cuneus and medial premotor regions without accompanying task-related differences in MRI signal amplitude in these areas. Contrasts of signal amplitude did reveal greater activity associated with the non-standard task relative to the standard task in the right inferior parietal lobule and a portion of the left superior posterior cerebellum. The findings of this study shed light on brain regions involved in overcoming our default tendency to spatially couple eye and arm movements during visually-guided reaching. Further, the results suggest that the regions reported here may be important in neurological disorders such as optic ataxia, Alzheimer's disease, and mild cognitive impairment, which are associated with deficits in producing non-standard visuomotor mappings while leaving standard visuomotor mapping relatively intact.

Evidence for distinct brain networks in the control of rule-based motor behavior

Reach guidance when the spatial location of the viewed target and hand movement are incongruent (i.e., decoupled) necessitates use of explicit cognitive rules (strategic control) or implicit recalibration of gaze and limb position (sensorimotor recalibration). In a patient with optic ataxia (OA) and bilateral superior parietal lobule damage, we recently demonstrated an increased reliance on strategic control when the patient performed a decoupled reach (Granek JA, Pisella L, Stemberger J, Vighetto A, Rossetti Y, Sergio LE. PLoS One 8: e86138, 2013). To more generally understand the fundamental mechanisms of decoupled visuomotor control and to more specifically test whether we could distinguish these two modes of movement control, we tested healthy participants in a cognitively demanding dual task. Participants continuously counted backward while simultaneously reaching toward horizontal (left or right) or diagonal (equivalent to top-left or top-right) targets with either veridical or rotated (90°) cursor feedback. By increasing the overall neural load and selectively compromising potentially overlapping neural circuits responsible for strategic control, the complex dual task served as a noninvasive means to disrupt the integration of a cognitive rule into a motor action. Complementary to our previous results observed in patients with optic ataxia, here our dual task led to greater performance deficits during movements that required an explicit rule, implying a selective disruption of strategic control in decoupled reaching. Our results suggest that distinct neural processing is required to control these different types of reaching because in considering the current results and previous patient results together, the two classes of movement could be differentiated depending on the type of interference.

Reduced regional brain cortical thickness in patients with heart failure

AIMS

Autonomic, cognitive, and neuropsychologic deficits appear in heart failure (HF) subjects, and these compromised functions depend on cerebral cortex integrity in addition to that of subcortical and brainstem sites. Impaired autoregulation, low cardiac output, sleep-disordered-breathing, hypertension, and diabetic conditions in HF offer considerable potential to affect cortical areas by loss of neurons and glia, which would be expressed as reduced cortical thicknesses. However, except for gross descriptions of cortical volume loss/injury, regional cortical thickness integrity in HF is unknown. Our goal was to assess regional cortical thicknesses across the brain in HF, compared to control subjects.

METHODS AND RESULTS

We examined localized cortical thicknesses in 35 HF and 61 control subjects with high-resolution T1-weighted images (3.0-Tesla MRI) using FreeSurfer software, and assessed group differences with analysis-of-covariance (covariates; age, gender; p<0.05; FDR). Significantly-reduced cortical thicknesses appeared in HF over controls in multiple areas, including the frontal, parietal, temporal, and occipital lobes, more markedly on the left side, within areas that control autonomic, cognitive, affective, language, and visual functions.

CONCLUSION

Heart failure subjects show reduced regional cortical thicknesses in sites that control autonomic, cognitive, affective, language, and visual functions that are deficient in the condition. The findings suggest chronic tissue alterations, with regional changes reflecting loss of neurons and glia, and presumably are related to earlier-described axonal changes. The pathological mechanisms contributing to reduced cortical thicknesses likely include hypoxia/ischemia, accompanying impaired cerebral perfusion from reduced cardiac output and sleep-disordered-breathing and other comorbidities in HF.

Gaze locations affect explicit process but not implicit process during visuomotor adaptation

The role of vision in implicit and explicit processes involved in adaptation to novel visuomotor transformations is not well-understood. We manipulated subjects' gaze locations through instructions during a visuomotor rotation task that established a conflict between implicit and explicit processes. Subjects were informed of a rotated visual feedback (45° counterclockwise from the desired target) and instructed to counteract it by using an explicit aiming strategy to the neighboring target (45° clockwise from the target). Simultaneously, they were instructed to gaze at either the desired target (target-gaze group), the neighboring target (hand-target-gaze group), or anywhere (free-gaze group) during aiming. After initial elimination of behavioral errors caused by strategic aiming, the subjects gradually overcompensated the rotation in the early practice, thereby increasing behavioral errors (i.e., a drift). This was caused by an implicit adaptation overriding the explicit strategy. Notably, prescribed gaze locations did not affect this implicit adaptation. In the late practice, the target-gaze and free-gaze groups reduced the drift, whereas the hand-target-gaze group did not. Furthermore, the free-gaze group changed gaze locations for strategic aiming through practice from the neighboring target to the desired target. The onset of this change was correlated with the onset of the drift reduction. These results suggest that gaze locations critically affect explicit adjustments of aiming directions to reduce the drift by taking into account the implicit adaptation that is occurring in parallel. Taken together, spatial eye-hand coordination that ties the gaze and the reach target influences the explicit process but not the implicit process.

Distant functional connectivity for bimanual finger coordination declines with aging: an fMRI and SEM exploration

Although bimanual finger coordination is known to decline with aging, it still remains unclear how exactly the neural substrates underlying the coordination differ between young and elderly adults. The present study focused on: (1) characterization of the functional connectivity within the motor association cortex which is required for successful bimanual finger coordination, and (2) to elucidate upon its age-related decline. To address these objectives, we utilized functional magnetic resonance imaging (fMRI) in combination with structural equation modeling (SEM). This allowed us to compare functional connectivity models between young and elderly age groups during a visually guided bimanual finger movement task using both stable in-phase and complex anti-phase modes. Our SEM exploration of functional connectivity revealed significant age-related differences in connections surrounding the PMd in the dominant hemisphere. In the young group who generally displayed accurate behavior, the SEM model for the anti-phase mode exhibited significant connections from the dominant PMd to the non-dominant SPL, and from the dominant PMd to the dominant S1. However, the model for the elderly group's anti-phase mode in which task performance dropped, did not exhibit significant connections within the aforementioned regions. These results suggest that: (1) the dominant PMd acts as an intermediary to invoke intense intra- and inter-hemispheric connectivity with distant regions among the higher motor areas including the dominant S1 and the non-dominant SPL in order to achieve successful bimanual finger coordination, and (2) the distant connectivity among the higher motor areas declines with aging, whereas the local connectivity within the bilateral M1 is enhanced for the complex anti-phase mode. The latter may underlie the elderly's decreased performance in the complex anti-phase mode of the bimanual finger movement task.

Decoupled visually-guided reaching in optic ataxia: differences in motor control between canonical and non-canonical orientations in space

Guiding a limb often involves situations in which the spatial location of the target for gaze and limb movement are not congruent (i.e. have been decoupled). Such decoupled situations involve both the implementation of a cognitive rule (i.e. strategic control) and the online monitoring of the limb position relative to gaze and target (i.e. sensorimotor recalibration). To further understand the neural mechanisms underlying these different types of visuomotor control, we tested patient IG who has bilateral caudal superior parietal lobule (SPL) damage resulting in optic ataxia (OA), and compared her performance with six age-matched controls on a series of center-out reaching tasks. The tasks comprised 1) directing a cursor that had been rotated (180° or 90°) within the same spatial plane as the visual display, or 2) moving the hand along a different spatial plane than the visual display (horizontal or para-sagittal). Importantly, all conditions were performed towards visual targets located along either the horizontal axis (left and right; which can be guided from strategic control) or the diagonal axes (top-left and top-right; which require on-line trajectory elaboration and updating by sensorimotor recalibration). The bilateral OA patient performed much better in decoupled visuomotor control towards the horizontal targets, a canonical situation in which well-categorized allocentric cues could be utilized (i.e. guiding cursor direction perpendicular to computer monitor border). Relative to neurologically intact adults, IG's performance suffered towards diagonal targets, a non-canonical situation in which only less-categorized allocentric cues were available (i.e. guiding cursor direction at an off-axis angle to computer monitor border), and she was therefore required to rely on sensorimotor recalibration of her decoupled limb. We propose that an intact caudal SPL is crucial for any decoupled visuomotor control, particularly when relying on the realignment between vision and proprioception without reliable allocentric cues towards non-canonical orientations in space.

Acute alcohol consumption impairs controlled but not automatic processes in a psychophysical pointing paradigm

Numerous studies have investigated the effects of alcohol consumption on controlled and automatic cognitive processes. Such studies have shown that alcohol impairs performance on tasks requiring conscious, intentional control, while leaving automatic performance relatively intact. Here, we sought to extend these findings to aspects of visuomotor control by investigating the effects of alcohol in a visuomotor pointing paradigm that allowed us to separate the influence of controlled and automatic processes. Six male participants were assigned to an experimental "correction" condition in which they were instructed to point at a visual target as quickly and accurately as possible. On a small percentage of trials, the target "jumped" to a new location. On these trials, the participants' task was to amend their movement such that they pointed to the new target location. A second group of 6 participants were assigned to a "countermanding" condition, in which they were instructed to terminate their movements upon detection of target "jumps". In both the correction and countermanding conditions, participants served as their own controls, taking part in alcohol and no-alcohol conditions on separate days. Alcohol had no effect on participants' ability to correct movements "in flight", but impaired the ability to withhold such automatic corrections. Our data support the notion that alcohol selectively impairs controlled processes in the visuomotor domain.

Guidelines and quality measures for the diagnosis of optic ataxia

Since the first description of a systematic mis-reaching by Bálint in 1909, a reasonable number of patients showing a similar phenomenology, later termed optic ataxia (OA), has been described. However, there is surprising inconsistency regarding the behavioral measures that are used to detect OA in experimental and clinical reports, if the respective measures are reported at all. A typical screening method that was presumably used by most researchers and clinicians, reaching for a target object in the peripheral visual space, has never been evaluated. We developed a set of instructions and evaluation criteria for the scoring of a semi-standardized version of this reaching task. We tested 36 healthy participants, a group of 52 acute and chronic stroke patients, and 24 patients suffering from cerebellar ataxia. We found a high interrater reliability and a moderate test-retest reliability comparable to other clinical instruments in the stroke sample. The calculation of cut-off thresholds based on healthy control and cerebellar patient data showed an unexpected high number of false positives in these samples due to individual outliers that made a considerable number of errors in peripheral reaching. This study provides first empirical data from large control and patient groups for a screening procedure that seems to be widely used but rarely explicitly reported and prepares the grounds for its use as a standard tool for the description of patients who are included in single case or group studies addressing optic ataxia similar to the use of neglect, extinction, or apraxia screening tools.

A test revealing the slow acquisition and the dorsal stream substrate of visuo-spatial perception

We propose a battery of simple clinical tests to assess the development of elementary visuo-spatial perception. We postulate that most of the tasks we selected rely on the visual dorsal stream, although the dual-stream theory (Milner & Goodale, 1995) discards the role of the dorsal stream for visual perception. In order to test the contribution of this anatomical substrate in visuo-spatial perception, we evaluated the performance of two adult patients with acquired bilateral occipito-parietal (dorsal stream) damage. Additionally, the developmental evolution was assessed by testing 96 children from 4 to 12 years old (4 two-year age groups of 24 children). In order to determine the point at which children achieved adult performance, and to provide a control group for the two patients, we also tested a group of 14 healthy adults. The results highlighted the necessity for age-dependent normative values: adult performance was achieved only at the age of 8 for length and size comparisons and at 12 for dot localisation. In contrast, the ability to judge angles and midlines did not reach adult performance even in the oldest group of children, suggesting further acquisition through adolescence. Occipito-parietal lesions strongly and differentially affected elementary visuo-spatial tasks. In overall scores, the two adult patients were approximately at the level of 6-year olds, below the outlier limit of the adult group. They were on average within the adult interquartile range for processing length and size but clearly outside for the 4 other subtests (Angle, Midline, Position perception and Position selection). As a whole, these data both shed light on the neuroanatomical bases of visuo-spatial perception and allow for age-specific comparisons in children with developmental disorders potentially linked to visuo-spatial and/or attentional defects.