Is the Medial Posterior Parietal Area V6A a Single Functional Area?

Abstract

The visuomotor medial posterior parietal area V6A has been recently subdivided into two cytoarchitectonic sectors called V6Ad and V6Av (Luppino et al., 2005). The aim of the present study was to recognize whether these two cortical sectors show different functional profiles. Fourteen hemispheres from eight animals (Macaca fascicularis) were included in this study, for a total of 3828 extracellularly recorded neurons assigned to areas V6Ad or V6Av on cytoarchitectural basis. The sensitivity of recorded neurons to sensory-and motor-related activities was checked with a series of functional tests performed on behaving animals. We found that cells sensitive to visual stimuli were more represented in V6Av and cells sensitive to somatosensory stimuli were more represented in V6Ad. Visual cells directly encoding spatial locations (real-position cells) were present only in V6Av. Cells encoding basic visual and somatic properties as well as different aspects of reaching and grasping activities were present in both sectors of V6A, although with different incidence. Cells that had reach-related activity enhanced by visual feedback and grasping neurons activated by whole-hand prehension were more concentrated in V6Av. Conversely, reaching neurons inhibited by visual feedback and grasping neurons activated by precision grip were more represented in V6Ad. Although V6Av and V6Ad show partly different functional profiles, our data support the idea that V6A is a single functional area involved in the control of reach-to-grasp movements, with the dorsal sector (V6Ad) more involved in the somatomotor control and the ventral sector (V6Av) in the visual control of reaching and grasping actions.

Eye Position Encoding in Three-Dimensional Space: Integration of Version and Vergence Signals in the Medial Posterior Parietal Cortex

“…Since ϳ60% of V6A neurons are responsive to visual stimulation (Galletti et al, 1996;Gamberini et al, 2011), it could be that the precocious fixation-related discharges we observed are actually visual responses to the fixation-LED appearance. To check this possibility, we compared in single cells the activity during FIX in the preferred position with that recorded when the monkey was sporadically fixating at that same location at the beginning of the trial, before LED onset (Student's t test, p Ͻ 0.05).…”

“…The anatomical reconstruction of recording sites was performed using the cytoarchitectonic criteria described by Luppino et al (2005) and the functional criteria detailed by Galletti et al (1999a) and Gamberini et al (2011). Figure 3A is a posterolateral view of the partially dissected macaque brain that shows the location of area V6A.…”

“…Figure 6 shows two examples of cells affected by version ( A) or vergence ( B) only. The neuron shown in Figure 6 A was Gamberini et al, 2011). The inferior parietal lobule of the right hemisphere has been cut away at the level of the fundus of the intraparietal sulcus to show the cortex of the medial bank of this sulcus.…”

Vision for Action in the Macaque Medial Posterior Parietal Cortex

“…In all cases, one section of every five was stained with the Nissl method (thionin, 0.1% in 0.1 M acetate buffer, pH 3.7) for the cytoarchitectonic analysis. Procedures to reconstruct microelectrode penetrations and to assign neurons recorded in the anterior bank of the parieto-occipital sulcus to area V6A were as those previously described by our group (Galletti et al, 1996(Galletti et al, , 1999a(Galletti et al, , 1999bGamberini et al, 2011). Briefly, electrode tracks and the approximate location of each recording site were reconstructed on histological sections of the brain on the basis of the lesions and several other cues, such as the coordinates of penetrations within the recording chamber, the kind of cortical areas passed through before reaching the region of interest, and the depths of passage points between gray and white matter.…”

“…It has been reported that area V6A contains visual neurons that are very sensitive to the orientation of visual stimuli (Galletti et al, 1996(Galletti et al, , 1999aGamberini et al, 2011), thus providing critical information for object grasping .…”