Tactile discrimination capacity in relation to size and organization of somatic sensory cortex in primates: I. Old-World prosimian, Galago; II. New-World anthropoids, Saimiri and Cebus

Abstract

Living primates vary considerably in brain organization, in sensorimotor and cognitive abilities, and in natural behavioral repertoires. Comparative studies of primary (SI) and secondary (SII) somatic sensory cortex of primates reveal major differences in the size and in the complexity of topographic projection patterns. The separate projections of the glabrous hand to SI cytoarchitectonic areas 3b and 1 described in the Old World (OW) anthropoid Macaca and in New World (NW) anthropoids Cebus, Saimiri, and Aotus are lacking in NW Saguinus and in the prosimian Galago. The relationship between the size and complexity of SI organization and tactile abilities is explored in this study of four species of primates--Galago, Macaca, Cebus, and Saimiri. These species were trained to discriminate between pairs of objects differing either in cross-sectional diameter (size) or surface roughness (texture). The course of acquisition of such tactile discrimination in normal Macaca and the nature of deficits following SI or SII removals are known. Selective lesions of either cytoarchitectonic area 1 or 2 in Macaca affect only texture or size discriminations, respectively. Removal of area 3b in SI, or of SII, in Macaca affects both size and texture capacities. The single projection of the glabrous hand to area 3b-1 of Galago led to our expectation that the capacity of Galago to discriminate textures would be more similar to an area 1-lesioned than to a normal Macaca. The substantial and persistent differences between Macaca and Galago on texture, but not size, tasks lend support to the view that the evolution of a second projection of the glabrous hand to area 1 in Macaca contributes to increased texture discrimination capacity. The similarity in multiple projection patterns of the glabrous hand to areas 3b and 1 in Macaca, Saimiri, and Cebus led us to expect greater correspondence in texture discrimination capacity between these three anthropoids than to Galago. Contrary to expectations, Saimiri and Cebus showed a tactile capacity more similar to Galago than to Macaca. Furthermore, the texture discrimination capacity of Cebus actually improved substantially after removal of area 1. This provides further evidence, together with the single SI hand area in NW Saguinus and Galago, that the separate cutaneous projections to area 1 in OW and NW primates are not homologous but evolved independently and possibly serve different tactile functions.

Object grasping and manipulation in capuchin monkeys (genera Cebus and Sapajus)

“…It has been supposed that the enlarged brain and spinal cord area convey an augmented number of sensorimotor fibres to support the manual dexterity and manipulative skills of capuchins (Rilling & Insel, 1999). At the cortical level, capuchins have the following characteristics: (1) well-differentiated somatosensory maps of the hands, particularly for the glabrous skin of palms and digits (Carlson & Nystrom, 1994); (2) multiple premotor areas in the frontal lobe (Dum & Strick, 2005); and (3) well-differentiated parietal area 2, associated with proprioception, and area 5, associated with motor planning and internal body coordinates for visually guided reaching, grasping and manipulation (Padberg et al, 2007). Interestingly, both the location and the organization of parietal areas 2 and 5 more closely resemble those of macaques (Pons et al, 1985), i.e.…”

The dating of linguistic beginnings

“…With regard to the somatosensory component of the feedback loop, Carlson and Nystrom (1994) report similarly discrepant organizational properties between these two species at the level of the neocortex. The primary somatosensory map of the Cebus apella hand area includes a discrete and extensive representation of the individual digits whereas the hand representation of Saimiri sciureus is significantly less differentiated, with coextensive finger and palm representations.…”

Uma mão ajuda a outra: desenvolvimento da coordenação bimanual em>i<Sapajus libidinosus>/i< selvagens

“…Fragaszy et al (2004) os classificam como forrageadores extrativistas hábeis, pois conseguem utilizar um vasto repertório de habilidades manuais para acessar e processar alimentos e contornar obstáculos do ambiente. Essas habilidades são apoiadas por uma série de adaptações neuroanatômicas: (1) cérebro e medula espinhal grandes para o tamanho do seu corpo, possivelmente suportando maior quantidade de fibras sensório-motoras que percorrem a medula (Rilling & Insel, 1999); (2) dispõem de mapas somatossensoriais bem diferenciados na pele glabra das palmas das mãos e dedos (Carlson & Nystrom, 1994); (3) os músculos do antebraço possuem semelhanças importantes aos humanos, principalmente aqueles que atuam no movimento do dedo polegar (Aversi-Ferreira et al, 2011); (4) apresentam um substrato abundante de motoneurônios corticoespinhais que inervam os dígitos da mão (Bortoff & Strick, 1993) e (5) possuem áreas corticais associadas a propriocepção e planejamento motor bem desenvolvidas (Padberg et al, 2007).…”