P1 ARS ary P2 ARS plb December 15 1998 QC ARS anil 12 35 T1 ARS Annual Reviews AR076 14 Annu Rev Neurosci 1999 22 319 49 Annu Rev Neurosci 1999 22 319 349 Downloaded from arjournals annualreviews org by University of Texas Austin on 09 10 07 For personal use only SPACE AND ATTENTION IN PARIETAL CORTEX Carol L Colby Department of Neuroscience and Center for the Neural Basis of Cognition University of Pittsburgh Pittsburgh Pennsylvania 15260 Michael E Goldberg Laboratory of Sensorimotor Research National Eye Institute Bethesda MD 20892 and Department of Neurology Georgetown University School of Medicine Washington DC 20007 KEY WORDS saccadic eye movements spatial representation spatial perception ABSTRACT The space around us is represented not once but many times in parietal cortex These multiple representations encode locations and objects of interest in several egocentric reference frames Stimulus representations are transformed from the coordinates of receptor surfaces such as the retina or the cochlea into the coordinates of effectors such as the eye head or hand The transformation is accomplished by dynamic updating of spatial representations in conjunction with voluntary movements This direct sensory to motor coordinate transformation obviates the need for a single representation of space in environmental coordinates In addition to representing object locations in motoric coordinates parietal neurons exhibit strong modulation by attention Both topdown and bottom up mechanisms of attention contribute to the enhancement of visual responses The saliance of a stimulus is the primary factor in determining the neural response to it Although parietal neurons represent objects in motor coordinates visual responses are independent of the intention to perform specific motor acts The US Government has the right to retain a nonexclusive royalty free license in and to any copyright covering this paper 319 P1 ARS ary P2 ARS plb December 15 1998 320 QC ARS anil 12 35 T1 ARS Annual Reviews AR076 14 COLBY GOLDBERG Annu Rev Neurosci 1999 22 319 349 Downloaded from arjournals annualreviews org by University of Texas Austin on 09 10 07 For personal use only INTRODUCTION Space is a supramodal construct not limited to a specific sensation We can estimate an object s spatial location from many different sensory cues but only with our own movement can the accuracy of that estimation be determined Although space must be calculated from sensation and calibrated by movement it is not necessarily linked to any specific sensation or movement Thus we can identify a spatial location by sight sound or touch and we can look at it or reach for it with either hand Even Shakespeare understood this In King Lear Regan invites the newly blinded Gloucester to smell his way to Dover Act III scene vii The nature of the brain s spatial representation has been the subject of much debate see Stein 1992 though the parietal lobe is considered crucial for that representation Critchley 1953 In this review we consider how space is represented in the parietal cortex of humans and monkeys and how that representation is related to the generation of movement and to the more general process of visuospatial attention MULTIPLE REPRESENTATIONS OF SPACE IN PARIETAL CORTEX The traditional view of the representation of space supported by subjective experience is that we construct a single spatial map of the world in which objects and actions are represented in a unitary framework The alternative view holds that the brain constructs multiple spatial representations with each representation linked to a different action or region of space Arbib 1991 Colby Duhamel 1991 1996 Fogassi et al 1996 Graziano et al 1994 Jeannerod et al 1995 While each spatial representation may be related to a specific class of actions it is not clear whether the parietal lobe actually plans those actions Snyder et al 1997 or only provides the sensory substrate for them Goodale Milner 1992 Behavioral and neuropsychological studies in humans indicate that multiple spatial reference frames are used to guide behavior and that parietal cortex is central to the construction of these representations Patients with lesions of the parietal lobe exhibit a variety of spatial deficits The most striking of these is neglect the tendency to ignore objects in the half of space opposite the side of the lesion Bisiach Vallar 1988 Heilman 1979 A patient with a right parietal lobe lesion may fail to notice or respond to objects on the left including food on the left side of a plate or words on the left side of a page Neglect occurs in all sensory modalities and can be expressed relative to any of several spatial reference frames including retinocentric body centered and environmentcentered These deficits in spatial perception are matched by corresponding P1 ARS ary P2 ARS plb December 15 1998 QC ARS anil 12 35 T1 ARS Annual Reviews AR076 14 Annu Rev Neurosci 1999 22 319 349 Downloaded from arjournals annualreviews org by University of Texas Austin on 09 10 07 For personal use only SPACE AND ATTENTION 321 deficits in the generation of spatially directed actions For example neglect can be specific for stimuli presented at particular distances Some patients tend to ignore stimuli presented near the body in peripersonal space while responding normally to distant stimuli or vice versa Bisiach et al 1986 Cowey et al 1994 Halligan Marshall 1991 Distance specific neglect may be apparent only when the subject must produce a motor response to the stimulus and not when spatial perception alone is tested Pizzamiglio et al 1989 The variety of deficits observed following parietal lobe damage suggests that parietal cortex must contain more than one kind of spatial representation Physiological and anatomical studies in monkeys have provided direct evidence that parietal cortex contains several separate functional areas and multiple representations of space Andersen et al 1997 Caminiti et al 1996 Colby Duhamel 1991 1996 Colby et al 1988 Jeannerod et al 1995 Lacquaniti et al 1995 Rizzolatti et al 1997 Stein 1992 Figures 1 and 2 The anatomical connections between parietal areas and their cortical targets provide some insight into the spatial reference frames served Parietal cortical areas are strongly linked with areas of prefrontal cortex premotor cortex and the frontal and supplementary eye fields which themselves encode object locations in relation to a variety of reference frames Gentilucci et al
View Full Document
Unlocking...