The second problem has been the averaging of responses over several distinct cell classes. We know that cortex comprises many different cell types (Connors and Gutnick, 1990, Markram et al., 2004 and Peters and Jones, 1984), which mediate different functions within circuits. One means of distinguishing cell classes is by the shapes of their extracellularly recorded spikes (Barthó et al., 2004, Mitchell et al., 2007 and Niell and Stryker, 2008). Data

indicate that neurons that generate narrow spikes correspond primarily to fast-spiking inhibitory cells, whereas broad-spiking neurons correspond primarily to excitatory pyramidal cells (Barthó et al., 2004, Henze et al., 2000, Kawaguchi and Kubota, 1997, ZD1839 McCormick et al., 1985 and Nowak et al., 2003). No studies to date, however, have probed the potential differential effect of visual experience on distinct cell classes in ITC. Here, we show that experience caused putative excitatory neurons to respond much more robustly to their best familiar compared to their best novel stimuli. In contrast, familiarity caused a dramatic decrease in the maximum and average rates of putative inhibitory neurons. Together, the results suggest that visual experience can profoundly alter visual object representations in ITC. To understand how

long-term sensory input sculpts the responses of individual ITC neurons, we first familiarized selleck inhibitor each of two monkeys with 125 color images of real-world objects (Hemera Photo-Objects: Vol. 1, 2, and 3) (see Figure S1A available online). The monkeys were trained to both passively G protein-coupled receptor kinase fixate the stimuli and to perform a short-term memory task with them. This exposure phase lasted between 3 months (monkey I) and 12 months (monkey D), resulting in an estimated number of exposures equal to 1,000 (monkey I) and 3,000

(monkey D) repetitions per image, split roughly evenly between the two tasks. Once familiarization was completed, we recorded the activity of well-isolated single units in ITC (n = 50 from monkey D; n = 38 from monkey I) in a passive fixation task (Figure 1A). Each neuron was screened with 125 familiar and 125 novel stimuli. The 125 novel stimuli were picked randomly on a daily basis from the same database as the familiar set (for examples, see Figures S1B–S1D). We recorded all units deemed visual by inspection of online stimulus-locked rastergrams. Both monkeys provided qualitatively similar data, so the results have been combined across subjects. Any notable differences are acknowledged (see Figure S3 for the main results split by monkey). As a means of correlating visual response properties with specific cell classes, we characterized the recorded sample of single units by the trough-to-peak widths of their extracellular spike waveforms (Figures 1B and 1C). Consistent with previous studies (Diester and Nieder, 2008, Hussar and Pasternak, 2009 and Mitchell et al.