P. P. Battaglini

Eye Position Influence on the Parieto-occipital Area PO (V6) of the Macaque Monkey

The aim of this work was to study the effect of eye position on the activity of neurons of area PO (V6), a cortical region located in the most posterior part of the superior parietal lobule. Experiments were carried out on three awake macaque monkeys. Animals sat in a primate chair in front of a large screen, and fixated a small spot of light projected in different screen locations while the activity of single neurons was extracellularly recorded. Both visual and non‐visual neurons were found. About 48% of visual and 32% of non‐visual neurons showed eye position‐related activity in total darkness, while in ˜61% of visual neurons the visual response was modulated by eye position in the orbit. Eye position fields and/or gain fields were different from cell to cell, going from large and quite planar fields up to peak‐shaped fields localized in more or less restricted regions of the animals field of view. The spatial distribution of fixation point locations evoking peak activity in the eye position‐sensitive population did not show any evident laterality effect, or significant top/bottom asymmetry. Moreover, the cortical distribution of eye position‐sensitive neurons was quite uniform all over the cortical region studied, suggesting the absence of segregation for this property within area PO (V6). In the great majority of visual neurons, the receptive field‘moved’with gaze according to eye displacements, remaining at the same retinotopic coordinates, as is usual for visual neurons. In some cases, the receptive field did not move with gaze, remaining anchored to the same spatial location regardless of eye movements (‘real‐position cells). A model is proposed suggesting how eye position‐sensitive visual neurons might build up real‐position cells in local networks within area PO (V6). The presence in area PO (V6) of real‐position cells together with a high percentage of eye position‐sensitive neurons, most of them visual in nature, suggests that this cortical area is engaged in the spatial encoding of extrapersonal visual space. Since lesions of the superior parietal lobule in humans produce deficits in visual localization of targets as well as in arm‐reaching for them, and taking into account that the monkeys area PO (V6) is reported to be connected with the premotor area 6, we suggest that area PO (V6) supplies the premotor cortex with the visuo‐spatial information required for the visual control of arm‐reaching movements.

Parietal neurons encoding spatial locations in craniotopic coordinates

The receptive fields of visual neurons are known to be retinotopically arranged, and in awake animals they “move” with gaze, maintaining the same retinotopic location regardless of eye position. Here, we report the existence in the monkey parietal cortex of cells (called “real-position” cells) whose receptive field does not systematically move with gaze. These cells respond to the visual stimulation of the same spatial location regardless of eye position and therefore directly encode visual space in craniotopic instead of retinotopic coordinates.

Arm Movement-related Neurons in the Visual Area V6A of the Macaque Superior Parietal Lobule

Area V6A is a cortical visual area located in the posterior face of the superior parietal lobule in the macaque monkey. It contains visual neurons as well as neurons not activated by any kind of visual stimulation. The aim of this study was to look for possible features able to activate these latter neurons. We tested 70 non‐visual V6A neurons. Forty‐three of them showed an arm movement–related neural discharge due to somatosensory stimulation and/or skeletomotor activity of the upper limbs of the animal. The arm movement‐related neural discharge started before the onset of arm movement, often before the earliest lectromyographic activity. Thus, although the discharge is probably supported by proprioceptive and tactile inputs it is not fully dependent on them. Arm movement‐related neurons of area V6A seem to be well equipped for integrating motor signals related to arm movements with somatosensory signals evoked by those ovements. Taking into account also the visual characteristics of V6A neurons, it seems likely that area V6A as a whole is involved in the visual guiding of reaching

Functional Properties of Neurons in the Anterior Bank of the Parieto-occipital Sulcus of the Macaque Monkey

Extracellular recordings were made in the anterior bank of the parieto‐occipital sulcus of two waking monkeys trained to perform fixation tasks in normal illumination or in complete darkness. Of the recorded neurons, 73% (251/343) were responsive to visual stimulation, but their overall organization did not conform to a simple, continuous retinotopic map. Most of the visual neurons showed a high degree of orientation and direction sensitivity, higher than that found in areas V1, V2 and V3A under the same experimental conditions. Whether they had a resolvable receptive field or not, the discharge rate of many neurons in the anterior bank of the parieto‐occipital sulcus was influenced by oculomotor activity. The animals were required to execute pursuit or saccadic eye movements in darkness. Saccadic eye movements were found to influence 19% of the neurons tested (29/156); by contrast, pursuit eye movements were without effect (0/64). Saccade responses were direction‐tuned and, in several cases, the neuronal discharge started before the onset of eye movement. The animals were also required to gaze, in darkness, at nine different positions on the screen they faced. Of the neurons tested, 59% (102/174) were affected by the direction of gaze. Higher discharge rates were generally observed when the animals looked towards the lower part of the field of view. Given the functional properties of its neurons, its connections with area V3A—where neural signals appropriate for building an objective map of the visual space are present (Galletti and Battaglini, 1989, J. Neurosci., 9, 1112–1125)—and its output to the visuomotor centres involved in the generation of saccades (frontal eye fields and superior colliculus), we infer that the cortex of the anterior bank of the parieto‐occipital sulcus might be part of the network involved in the control of gaze in order to locate objects in visual space.

Integrating perception and action through cognitive neuropsychology (broadly conceived).

This special issue of Cognitive Neuropsychology aims at providing a forum for empirical and theoretical research on the integration of perceptual and motor processes in the human mind. The initiative originated at a workshop on “Integrative approaches to perception and action” (Trieste, 27 October, 2006), a satellite event to the 14th Kanizsa Lecture. The 2006 lecture addressed the architecture of human vision from a broad perspective, reviewing a range of neuropsychological, imaging, and behavioural data to reveal the organization of visual pathways and relate it to the functions of vision. The satellite workshop presented alternative views and additional empirical findings, providing an exciting backdrop for the lecture. The number of valuable insights that ensued encouraged us to develop the project into a collection of printed papers. This special issue is the outcome of this process. Historically, the cognitive sciences have used the adjective “integrative” in different ways. The earliest dates back at least to the publication of Sherrington’s classic, The Integrative Action of the Nervous System (Sherrington, 1906), which aimed at studying how separate organs and body parts are brought together into a unified, organized organism by the workings of the nervous system. The integrative phenomena that came under Sherrington’s scrutiny were limited by his emphasis on reflexes as units of integration and by his corresponding interest in animal preparations displaying reflex behaviour (Levine, 2007). However, there is little doubt that understanding how different brain mechanisms relate to one another and to other bodily mechanisms, such as those mediating actions, remains central to contemporary cognitive science. A second sense refers to the need of integrating different levels of explanation when studying the mind/brain. Indeed, the idea that approaches limited to a single level of analysis do not suffice to unravel how the brain works forms the core dictum of integrative neuroscience

Cortical mechanisms for visual perception of object motion and position in space.

The present review is aimed at analyzing and discussing some of the cortical mechanisms possibly involved in the perception of object motion and object localization in the visual field. A comprehensive approach to these topics would be beyond the scope of this work. The highest priority, therefore, will be given to the cortical machinery involved in these processes, while very little (or nothing at all) will be said on the possible role played by subcortical structures such as the lateral geniculate nucleus and the superior colliculus which, albeit not directly involved in perception, might contribute to it.

Visuomotor deficits and fast recovery after area V6A lesion in monkeys.

In order to study the involvement of area V6A in visually guided behavior, restricted lesions to the anterior bank of the parieto-occipital sulcus (POs) were made in two adult Cercopithecus aethiops monkeys, trained in visuomotor tests. Beside the known clinical signs of parietal deficit (abnormal posture of the arm contralateral to the most recent lesion and reluctance to use it), misreaching was evident soon after surgery and disappeared quickly. Uncertainties in a landmark test and prolonged response times to the pressing of light-buttons lasted for a few weeks and 1 month, respectively. As suggested by previous anatomical and physiological data, these findings confirm the role of the POs region in the execution of reaching movements. Moreover, they also demonstrate that following lesion, locally networked areas can rapidly adjust in order to re-establish pre-lesional behavior. These adjustments take place well before that any anatomical changes may occur.