6, p < 0.001)—i.e., with temporal proximity from the motor response. This is to be expected from a response preparation signal driven by large temporal fluctuations in sensory
input ( Yang and Shadlen, 2007). We carried out additional analyses locked to the onset of the response period, which all confirmed that motor beta-band activity behaved as a response preparation signal (Figure S7): (1) the neural encoding of the sum of response updates distinguished correct choices from errors from more than 500 ms before the onset of the response period KU-55933 price (paired t test, t14 = 4.8, p < 0.001); (2) the neural decoding of choice (i.e., left- versus right-handed response) showed similar predictive profiles preceding correct choices and errors (see Supplemental Information); and (3) the between-element variability in neural encoding of response updates
correlated positively with Selleck CP690550 the between-element weighting profile estimated behaviorally (r = +0.44 ± 0.10, t test against zero, t14 = 4.4, p < 0.001). Finally, we assessed whether the neural encoding of DUk in motor beta-band activity also fluctuated rhythmically according to the phase of parietal delta oscillations (Figure 7C), and found that it followed the same phase relationship as its earlier encoding in broadband parietal signals (Rayleigh test, r14 = 0.50, p < 0.01). This phase dependency suggests that motor beta-band activity reflects a computation that occurs downstream from the weighting of momentary evidence according
to the phase of parietal delta oscillations. Together, these findings chart the electrophysiological substrates of the sensorimotor cascade whereby successive samples 3-mercaptopyruvate sulfurtransferase of sensory evidence are processed from lower to higher levels, integrated, and converted into an appropriate response. By linking trial-to-trial fluctuations in neural signals to variability in choice, these findings draw a clear distinction between the computations performed by two neural mechanisms during categorical decision making. First, momentary evidence undergoes a multiplicative weighting according to the phase of ongoing delta oscillations (1–3 Hz) overlying human parietal cortex. Subsequently, lateralized beta-band activity (10–30 Hz) over the motor cortex integrates the weighted evidence in an additive fashion, consistent with the formation of a decision variable. Categorical choices are thus preceded by discrete central and motor stages, both of which follow an early perceptual stage confined to early visual cortex. These findings thus call into question the widely held view that evidence accumulation is indistinguishable from the gradual engagement of a response effector—in other words, that the neural encoding of decision-relevant evidence reduces to a preparatory signal that precedes motor output ( Shadlen and Newsome, 2001; Roitman and Shadlen, 2002; Gold and Shadlen, 2003, 2007).