This suggests that expectation and attentional task-set may be partly distinct processes, as has been previously argued (Summerfield and Egner, 2009). Although the relationship between neuronal excitation and inhibition and the hemodynamic (or metabolic) response is equivocal and multifaceted Androgen Receptor Antagonist (Logothetis, 2008), the activity reductions observed here for expected stimuli likely reflect a reduction of neural activity. This is in line with recent neurophysiological studies in monkeys and humans, highlighting that valid expectations lead to a reduction in spiking activity (Meyer and Olson, 2011) as well as gamma-band oscillatory activity (Todorovic et al., 2011). Additionally, a recent combined hemodynamic/neurophysiological

study reported hemodynamic and metabolic downregulation following neuronal inhibition in the visual cortex of monkeys (Shmuel et al., 2006). In sum, our data provide evidence for how expectations facilitate perceptual inference in a noisy

and ambiguous visual world by sharpening early sensory representations. Twenty healthy right-handed individuals (sixteen female, age 22 ± 4, mean ± SD) with normal or corrected-to-normal vision gave written informed consent to participate in this study, in accordance with the institutional guidelines of the local ethics committee (CMO region Arnhem-Nijmegen, The Netherlands). learn more Data from one subject were excluded due to excessive head movement, and one subject was excluded due to failure to comply with task tuclazepam instructions. Grayscale luminance-defined sinusoidal grating stimuli were generated using MATLAB (MathWorks, Natick, MA) in conjunction with the Psychophysics Toolbox (Brainard, 1997), and displayed on a rear-projection screen using a luminance-calibrated EIKI projector (1,024 × 768 resolution, 60 Hz refresh rate). Gratings were displayed in an annulus (outer

diameter: 15° of visual angle, inner diameter: 3°), surrounding a fixation point. The auditory cue consisted of a pure tone (450 or 1,000 Hz), presented over MR-compatible earphones. Each trial consisted of an auditory cue, followed by two consecutive grating stimuli (Figure 1). The two grating stimuli were presented for 500 ms each, separated by a blank screen (100 ms). The auditory cue consisted of either a low- (450 Hz) or high-frequency (1000 Hz) tone, which predicted the orientation of the subsequent grating stimuli (∼45° or ∼135°) with 75% validity. The contingencies between cues and gratings were flipped halfway through the experiment, and the order was counterbalanced over subjects. In separate runs (128 trials, ∼14 min), subjects performed either an orientation or a contrast discrimination task on the two gratings. The first grating had an orientation of either 45° or 135° (±a Gaussian jitter, drawn from a normal distribution with mean = 0 and standard deviation = 1) and a luminance contrast of 80%.