Visual responses to targets and distracters by inferior temporal neurons after lesions of extrastriate areas V4 and TEO Giuseppe Bertini, 1,3,CA Elizabeth A. Bu¡alo, 2 Peter De Weerd, 1,4 Robert Desimone 2 and Leslie G. Ungerleider 1 1 Laboratory of Brain and Cognition, NIMH, 10 Center Drive; 2 Laboratory of Neuropsychology, NIMH, 49 Convent Drive, Bethesda, MD 20892, USA 3 Present address: Department of Morphological and Biomedical Sciences, University of Verona, Strada le Grazie 8, 37134 Verona, Italy 4 Present Address: Psychology Department, Neurocognition Group, University of Maastricht, The Netherlands CA Corresponding Author: giuseppe.bertini@univr.it Received 7 April 2004; accepted 20 May 2004 DOI: 10.1097/01.wnr.0000134847.86625.15 While lesions of visual areas V4 and TEO only modestly a¡ect dis- crimination of isolated objects, they signi¢cantly impair the ability to selectively attend to an object surrounded by distracters.To test whether such de¢cits result from a loss of inputs to higher order areas, we recorded from area TE neurons after removing portions of V4 and TEO in a monkey. Responses to isolated targets in a le- sion-a¡ected visual quadrant were substantially preserved, indicat- ing that TE still receives information even after removing a major source of input. Distracters increased or decreased the response to targets more in the lesion-a¡ected than in the normal quadrant, supporting the idea that V4 and/orTEO are sites where top-down attentional inputs ¢lter out distracting stimuli. NeuroReport 15:1611^1615  c 2004 Lippincott Williams & Wilkins. Key words: Attention; Electrophysiology; Receptive ¢eld; Rhesus monkey; Visual cortex; Visual perception INTRODUCTION When attention is focused on a behaviorally relevant stimulus in the visual field, the processing of that object is enhanced relative to that of any surrounding distracters. Several electrophysiological studies have suggested that this comes about by the filtering of distracting stimuli from the receptive fields of neurons along the ventral processing stream, an occipitotemporal cortical pathway that is critical for visual object recognition in primates [1–4]. The important role of ventral stream areas in attentional filtering is also supported by several lesion studies [5–11]. In particular, De Weerd et al. [9,11] found that lesions of extrastriate areas V4 and/or TEO produced a severe impair- ment in the discrimination of a variety of target stimuli when they were surrounded by salient luminance distracters, whereas the discrimination of the same stimuli posed little difficulty in the absence of distracters. Similar results have been found in a human patient with a V4 lesion [12]. Because areas V4 and TEO provide the main input to inferior temporal area TE, the next processing stage in the ventral stream [13,14], one possible explanation for the behavioral results is that V4 and TEO lesions simply deprive TE of visual input, essentially deafferenting the highest levels of the ventral stream. In that case, object discrimina- tion might be mediated by alternative pathways that do not have the capacity to both process object features and filter out distracting stimuli from receptive fields. To test this, we recorded the responses of area TE neurons to target stimuli presented either in a visual quadrant affected by a combined V4 and TEO lesion, or in an unaffected quadrant. If TE neurons did continue to respond to visual input in the absence of V4 and TEO, the next step would be to test whether the TE neurons would show reduced efficiency in filtering out distracting information from their receptive fields. We planned to test this by comparing neuronal responses in the normal and lesion-affected quadrants to stimuli presented either alone or surrounded by irrelevant distracters (Fig. 1d). We reasoned that if V4 and TEO were critical sites where top-down attentional inputs filtered distracters from receptive fields, then lesions of these areas would result in impaired attentional filtering by neurons in area TE, which receives inputs from these two areas. MATERIALS AND METHODS Lesions and recording procedure: One adult male monkey (Macaca mulatta, monkey M1 from ref. [9]), weighing B9 kg, was used. All surgical and behavioral procedures were carried out in accordance with National Institutes of Health guidelines, under a protocol approved by the National Institute of Mental Health Institutional Animal Care and Use Committee, and have been described in detail VISION, CENTRAL NEUROREPORT 0959-4965  c Lippincott Williams & Wilkins Vol 15 No 10 19 July 2004 1611 Copyright © Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.