Ventral premotor cortex = all agranular frontal cortex ventral to the spur of the arcuate sulcus. Patterns of cytochrome oxidase staining corresponded well with cytoarchitectonic parcellation of von Bonin and Bailey (1947), and their convention of "FA, FB, FC" was replaced with "F1, F2, F3" [Matelli, 1985 #11] Using this parcellation, PMv is divided by a line between the spur of the arcuate sulcus and the inferior precentral dimple into area F4 caudally and F5 rostrally. Area F5 has been further subdivided based on cytoarchitectonic and immunohistochemical findings into a small portion located on the posterior bank of the inferior arcuate sulcus (F5ab or arcuate bank), and the remiander on the cortical convexity adjacent to the arcuate sulcus (F5c or convexity)
SMI-32 neurofilament antibody: "PMvc was deinfed as having a staining pattern rather similar to that of M1, but with less numerous cells in layer V and a fainter layer III. This part of the PMv could not be additionally subdivided mediolaterally as reported by Geyer et al. (1998)." (Gabarnet, Meskenaite, and Hepp-Reymond, 1999)
Microstimulation and single-unit recording shows arm, neck, face and mouth movements are represented. Arm and axial movements are located medially, oral-facial movements laterally (Gentillucci et al., 1988), neurons discharge in relation to movement towards or away from the body, some oral-facial representation. Almost no representation of distal movements.
Bimodal neurons (56%) somatosensory (large receptive fields, on hand, face, upper body) & visual receptive fields (in peri-personal space, in register with tactile fields). Most visual receptive fields respond preferentially to stimuli directed toward the tactile receptive fields. In 70%, the position of the visual field is gaze-invariant. Visual receptive field also remains anchored to the tactile receptive field when the body position changes. (Graziano, Yap and Gross, 1994) (Graziano, Hu and Gross, 1997).
Unimodal neurons (44%) - typically tactile, almost no visual responses. Same somatosensory characteristics as bimodal neurons.
- Strong, reciprocal connections with VIP, with additional reciprocal parietal connections to PF, PE-ip, and SII.
- Connected more strongly with F3 (SMA proper) than with F6 (pre-SMA). In contrast, F5 is connected more strongly with F6 than F3. F5 also has prefrontal input, whereas F4 does not.
- Thalamocortical input is from VL-o, VL-c, VPL-o.
- Recieves Striopallidal input through the VL-o, in contrast to F5 which receives cerebellar input through its principal thalamocortical relay, Olszewski's area X (see (Geyer, Matelli, Luppino, & Zilles, 2000) for review).
* Brainstem and Spinal:
- Dorsal F4 (arm representation) sends projections to reticular formation and cervical spinal cord
- Ventral F4 (face representation) sends projections to facial nucleus
Encoding peri-personal space and transforming object locations into appropriate movements towards them.
"An interesting finding is that the PMvr (F5) could be subdivided into three parts, as previously suggested by Matelli et al. (1996) on the basis of various stainings. The most rostral and lateral one was without and SMI-32 immunoreactivity but with a semigranular layer IV and particularly well laminated staining patterns in adjacent sections stained for AChE, PV, CR, CO and a1- and a2- subunits of the GABA receptor (Fig. 3: 7). A caudal adjacent one had a weak SMI-32 immunoreactivity in layer III, and the most caudal and medial region at the level of the spur contained striking immunoreactivity in layer V (Fig. 3: 6 and 5 respectively). This small region can be compared with the region found in the fundus of the SPcS and looks like an island of scattered immunoreactive layer V pyramidal cells, similar but independent of M1 proper. This point is corroborated by functional data showing that within the arcuate spur, and also lateral to it, ICMS could elicit finger movements, even at relatively low currents (Hepp-Reymond et al., 1994; Gabernet et al. 1997)." (Gabarnet et al., 1999)
In general, F5 neurons discharge with specific goal-directed movements of the hand, mouth, or both. F5ab neurons have been subdivided into classes according to the action effective in triggering them: grasping, holding, tearing, manipulating. [Rizzolati, 1988 #3]. F5ab neurons also discharge to the presentation of 3D objects, even when no action upon the object is allowed (Murata et al., 1997).
Following independent inactivation of AIP and F5ab the principal deficit is a disruption of the preshaping of the hand during grasping, with a mismatch between the features of the object to be grasped and the posturing of finger movements.
Strongly interconnected with AIP, with additional connections to PFG and SII. Beyond this, it is not clear how connectivity differs between F5ab and F5c. F5 has more connections with prefrontal cortex than F4, and is more connected with F6 (pre-SMA) than F3 (SMA). Only a small subregion of F5 sends connections to F1, while nearly all of F4 projects there. F5 is involved in a different subcortical loop - a cerebellar-thalamic (area X) cortical loop - than F4 (which receives pallidal input via the ventrolateral thalamus).
Transformation of appropriate 3D properties of objects into hand formations - each time an object is observed, its visual features are "translated" into a vocabulary of motor acts.
F5c neurons are indistinguishable from F5ab neurons as far as motor properties are concerned. Visual responses are mainly to observation of actions similar to those encoded by the neuron ("mirror" neurons). Observing the agent alone or the object alone is ineffective. Visual triggering requires an interaction between agent and object (Rizzolatti and Arbib, 1998a).
Predominantly involved in a reciprocal loop with area PF. Also connected with AIP, and SII.
Internal representation of actions.
The precentral sulcus develops in humans from two separate primordia. Each has a horizontal branch which represents the superior frontal sulcus and the inferior frontal sulcus, respectively. Rizzolatti proposes that the superior frontal sulcus and superior precentral sulcus correspond to the monkey superior arcuate sulcus, and the inferior frontal suclus and the ascending branch of the inferior precentral sulcus correspond to the monkey inferior arcuate sulcus. The human descending branch of the inferior precentral sulcus corresponds to the inferior precentral dimple of the monkey (Rizzolatti, Luppino, and Matelli, 1998b).
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