REVIEWS nd.neglect is more fre after dama to the y co 号0u or right ng st rk,either beca on of n nin top-o indicated by hemispheric oEF network 1p d c Future ir for goal stimuhs-dii ore dosely the dysfunction of a target d ical re ship between of pn on-SD elati eas some aspects of eglect c n be related t ain the TP eside of spa in dir tion to a location s to the s the help to dar al (ef vith n deficit If this teral I eye-mo y of the dor ugh the ided by ab logues of t works in the h 15 99 EM mG3 01-1222 n he 的120 10 00 7619 URE REVIEWS UME 3|MARCH 2002213NATURE REVIEWS | NEUROSCIENCE VOLUME 3 | MARCH 2002 | 213 REVIEWS codes mainly for locations in the right visual field, but the right hemisphere codes for locations in both fields13, consistent with a right visual field bias after right￾hemisphere lesions. We suggest that right TPJ lesions might ‘functionally’ inactivate the right dorsal IPs–FEF network, either because of decreased input from the TPJ or because of damage to the underlying white matter. This functional inactivation might be exacerbated by a relative hyperactivation of the left IPs–FEF network, as indicated by hemispheric models of orienting115. Future directions The proposed functional distinction between neural systems for goal-directed and stimulus-driven orienting raises many questions for future research. One issue concerns the anatomical relationship between regions of the dorsal frontoparietal network that are involved in attending to spatial location and non-spatial features such as motion, attending to effectors and linking stim￾uli to effectors. Specifying these relationships will require detailed studies in single subjects. Another issue concerns the functional relationship between dorsal and ventral networks during stimulus-driven orienting. For example, topographical mapping in both the TPJ and the dorsal network might indicate the relative role of each in directing attention to a location during exoge￾nous orienting. Understanding spatial coding in both networks will also help to clarify the pathophysiology of neglect. It is also important to link these functional descriptions with neurophysiological and neurophar￾macological descriptions of the same brain systems. Goal-directed orienting is influenced by cholinergic drugs, whereas stimulus-driven alerting is modulated by noradrenergic drugs116. If this neuropharmaco￾logical–behavioural correlation maps onto the anatomy of the dorsal and ventral attentional networks, then we might be able to use this information to treat more effectively acquired (stroke, trauma) or developmental (attention deficit) disorders of attention. Finally, all of these issues will be aided by a better understanding of the homologues of these networks in the human and monkey. Second, neglect is more frequent after damage to the right than to the left hemisphere110. By contrast, activity in the IPs–FEF network is largely bilateral during spatial orienting to the left or right visual field10–12, and becomes only slightly right lateralized during stimulus process￾ing15,16. Activation of the right TPJ during stimulus detection is strongly lateralized to the right hemisphere, consistent with the hemispheric lateralization of neglect. Finally, patients with neglect have deficits primarily in stimulus detection rather than in top-down goal-directed orienting. Neglect patients can voluntarily direct atten￾tion to the contralesional side, consistent with sparing of the IPs–FEF network, and can use cognitive cues to anchor attention to the left visual space during their rehabilitation111. The impairment in neglect matches more closely the dysfunction of a target detection system than an endogenous orienting system, particularly when the stimuli are unattended and outside the focus of pro￾cessing112. This functional characterization is more con￾sistent with a disruption of the stimulus-driven ventral frontoparietal attention network. Whereas some aspects of neglect can be related to the TPJ, other aspects are more problematic. First, detection deficits in neglect show a gradient across the visual field. The deficit is worse at the most peripheral locations on the side of space opposite to the lesion (the left visual field), and decreases as the stimulus position moves towards the same side of space as the lesion113. However, as the right TPJ responds equally well to stim￾uli in the contralateral (left) and ipsilateral (right) visual fields10,21, at least for eccentricities of up to ten degrees, TPJ lesions might be expected to cause bilateral deficits. Second, the TPJ is not well activated by motor prepara￾tion or execution, whereas neglect patients clearly show a deficit in initiating arm movements contralesionally114. These aspects of neglect might reflect dysfunction of the ipsilateral IPs–FEF network. Dorsal regions of the IPs–FEF system, for example, are involved in arm- and eye-movement selection. Also, although the spatial topography of the dorsal network in humans has not been investigated in detail, there is some evidence for an asymmetrical coding of space. The left hemisphere 1. Eriksen, C. W. & Hoffman, J. E. The extent of processing of noise elements during selective encoding from visual displays. Percept. Psychophys. 14, 155–160 (1973). 2. Posner, M. I., Snyder, C. R. R. & Davidson, B. J. Attention and the detection of signals. J. Exp. Psychol. 109, 160–174 (1980). 3. Ball, K. & Sekuler, R. Models of stimulus uncertainty in motion perception. Psychol. Rev. 87, 435–469 (1980). 4. Egeth, H. E., Virzi, R. A. & Garbart, H. 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