How Is Grasping Modified by

Abstract. Once a small object is touched, somatosensory afferent information from the glabrous (nonhairy) skin on the palm of the hand becomes highly important in the regulation of the grasp forces and subsequent manipulation of the object. This chapter discusses recent findings related to how tactile afferent signals are integrated with automatic control to effect functionally adaptive actions during manipulative phases of grasping. Although the control appears to be executed principally on the basis of previously acquired neural programs that issue the appropriate functional muscle synergies, to successfully accomplish even the most elementary manipulative tasks there are a number of other important regulatory events that rely on tactile afferent signals. These may account for prompt corrections of various execution errors. Furthermore, these events represent anticipatory adjustments of program parameters relating to the physical properties of the object currently handled, i.e., by maintaining an updated internal brain representation of the relevant properties such as the weight and friction in relation to the skin. Somatosensory information may also provide trigger signals that are utilized for appropriate sequential release of the "new' ' muscle commands during multiphasic manipulative tasks