“…In this study we investigated the pattern of thalamic input to the layer 6 corticothalamic (CT) pyramidal cells, which are unusual in having dendrites in two thalamorecipient layers: basal dendrites in layer 6 and apical dendrites in layer 4. The CT cells can be monosynaptically excited by electrical stimulation of the thalamic relay cells (Gilbert, 1977;Ferster and Lindström, 1983;Martin and Whitteridge, 1984) and, like neurons in layer 4, most have simple receptive fields (Harvey, 1978(Harvey, , 1980Ferster and Lindström, 1983;Martin and Whitteridge, 1984;Grieve and Sillito, 1995) (but see Gilbert, 1977). In addition to their feedback to the thalamus, CT cells send a collateral projection to layer 4, where they form an estimated 9 -19 times more synapses than the thalamic afferents (Ahmed et al, 1994;Binzegger et al, 2004), mainly with spiny neurons (McGuire et al, 1984;Ahmed et al, 1994;Anderson et al, 1994;Binzegger et al, 2004).…”