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Fig. 2.6. Long-range lateral connections in the macaque. Lateral connections, also sometimes called horizontal or intrinsic connections, run parallel to the cortical surface. In the visual cortex they extend over several millimeters and sprout branches at intervals. The branches form a local cluster of connections to other cells in the region, as shown for this layer 3 pyramidal cell in the macaque visual cortex (injected with horseradish peroxidase: The dendrites are shown with thick lines and axon collaterals with thin lines, and the horizontal scale is approximately 2.3 mm). Such clusters occur only in regions with similar functional properties as the parent cell. Reprinted with permission from Gilbert et al. (1990; adapted from McGuire et al. 1991), copyright 1990 by Cold Spring Harbor Laboratory Press.