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

Encoding of visual targets during 3D reaching movements in human and non-human primates

The aim of my thesis was to investigate how reaching for visual targets placed in 3D space influences the coordinate frames and the kinematics in non-human and human primates. To this end, I conducted three studies. The first study was conducted on non-human primates to find the predominant reference frame of cells in a specific reach related area of the PPC (area PEc) while reaching towards targets placed at different depths and directions; we tested whether PEc reaching cells displayed hand- and/or body-centered coding of reach targets. We found that the majority of PEc neurons encoded targets in a mixed body/hand-centered reference frame. Our findings highlight a role for area PEc as intermediate node between the visually dominated area V6A and the somatosensory dominated area PE. The second study was conducted on healthy human subjects to find the reference frame used while reaching towards targets placed at different depths and directions. Our results revealed 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. The third study was conducted on a patient with a parietal cortex lesion who showed optic ataxia symptoms. Optic ataxia patients show deficits in visuo-manual guidance especially when reaching to targets located in the periphery of the visual field. By manipulating gaze position and hand position of visual reaching targets, placed at different depth and directions, we investigated how reaching in peripheral and central viewing conditions influenced the trajectories and reach errors of the patient and controls. Our results suggest that the reaching inaccuracies observed, in particular in the configurations where the direction of gaze and reach differed, are due to a disruption of the online correction mechanism and that the PPC is involved in these automatic corrections

Vascular Supply of the Cerebral Cortex is Specialized for Cell Layers but Not Columns.

The vascular supply to layers and columns was compared in macaque primary visual cortex (V1) by labeling red blood cells via their endogenous peroxidase activity. Alternate sections were processed for cytochrome oxidase to reveal "patches" or "blobs," which anchor the interdigitated column systems of striate cortex. More densely populated cell layers received the most profuse blood supply. In the superficial layers the blood supply was organized into microvascular lobules, consisting of a central venule surrounded by arterioles. Each vessel was identified as an arteriole or venule by matching it with the penetration site where it entered the cortex from a parent arteriole or venule in the pial circulation. Although microvascular lobules and cytochrome oxidase patches had a similar periodicity, they bore no mutual relationship. The size and density of penetrating arterioles and venules did not differ between patches and interpatches. The red blood cell labeling in patches and interpatches was equal. Moreover, patches and interpatches were supplied by an anastomotic pial arteriole system, with no segregation of blood supply to the two compartments. Often a focal constriction was present at the origin of pial arterial branches, indicating that local control of cortical perfusion may be accomplished by vascular sphincters

Mixed Body/Hand Reference Frame for Reaching in 3D Space in Macaque Parietal Area PEc

none6siEuropean Union Grants, FP6-IST-027574-MATHESIS and FP7- IST-217077-EYESHOTS, by PRIN from MIUR, by FIRB 2013 N. RBFR132BKP and Fondazione del Monte di Bologna e Ravenna, Italy. National Health and Medical Research Council Grant APP1020839 and APP1082144 (Australia)The neural correlates of coordinate transformations from vision to action are expressed in the activity of posterior parietal cortex (PPC). It has been demonstrated that among the medial-most areas of the PPC, reaching targets are represented mainly in hand-centered coordinates in area PE, and in eye-centered, body-centered, and mixed body/hand-centered coordinates in area V6A. Here, we assessed whether neurons of area PEc, located between V6A and PE in the medial PPC, encode targets in body-centered, hand-centered, or mixed frame of reference during planning and execution of reaching. We studied 104 PEc cells in 3 Macaca fascicularis. The animals performed a reaching task toward foveated targets located at different depths and directions in darkness, starting with the hand from 2 positions located at different depths, one next to the trunk and the other far from it. We show that most PEc neurons encoded targets in a mixed body/hand-centered frame of reference. Although the effect of hand position was often rather strong, it was not as strong as reported previously in area PE. Our results suggest that area PEc represents an intermediate node in the gradual transformation from vision to action that takes place in the reaching network of the dorsomedial PPC.mixedmixedPiserchia, Valentina; Breveglieri, Rossella; Hadjidimitrakis, Kostas; Bertozzi, Federica; Galletti, Claudio; Fattori, PatriziaPiserchia, Valentina; Breveglieri, Rossella; Hadjidimitrakis, Kostas; Bertozzi, Federica; Galletti, Claudio; Fattori, Patrizi

Reactivating fear memory under propranolol resets pre-trauma levels of dendritic spines in basolateral amygdala but not dorsal hippocampus neurons

Fear memory enhances connectivity in cortical and limbic circuits but whether treatments disrupting fear reset connectivity to pre-trauma level is unknown. Here we report that C56BL/6J mice exposed to a tone-shock association in context A (conditioning), and briefly re-exposed to the same tone-shock association in context B (reactivation), exhibit strong freezing to the tone alone delivered 48 h later in context B (long term fear memory). This intense fear response is associated with a massive increase in dendritic spines and phospho-Erk (p-ERK) signaling in basolateral amygdala (BLA) but neurons. We then show that propranolol (a central/peripheral β-adrenergic receptor blocker) administered before, but not after, the reactivation trial attenuates long term fear memory assessed drug free 48 h later, and completely prevents the increase in spines and p-ERK signaling in BLA neurons. An increase in spines, but not of p-ERK, was also detected in the dorsal hippocampus (DH) of the conditioned mice. DH spines, however, were unaffected by propranolol suggesting their independence from the ERK/β-ARs cascade. We conclude that propranolol selectively blocks dendritic spines and p-ERK signaling enhancement in the BLA; its effect on fear memory is, however, less pronounced suggesting that the persistence of spines at other brain sites decreases the sensitivity of the fear memory trace to treatments selectively targeting βARs in the BLA. © 2013 Vetere, Piserchia, Borreca, Novembre, Aceti and Ammassari-Teule