Other criteria are access to the motion evidence and access to the oculomotor system
(since the animal reports direction with a saccade to a target), but the responses should outlast the immediate responses of visual cortical neurons and they cannot precipitate an DAPT mw eye movement. The lateral intraparietal area (LIP) seemed an obvious candidate (Shadlen and Newsome, 1996 and Glimcher, 2001). LIP was defined as the part of Brodmann area 7 that projects to brain structures involved in the control of eye movements (Andersen et al., 1990). It receives input from the appropriate visual areas and the pulvinar, and its neurons are known to respond persistently through intervals of up to seconds when an animal is instructed—but required to withhold—a saccade to a target (Barash et al., 1991 and Gnadt and Andersen, 1988). It seems obvious that one could construct a task like a delayed eye movement and to substitute
a decision about motion for BVD-523 cell line the instruction. Under this condition, LIP neurons ought to, at the very least, signal the monkey’s answer in the delay period after the decision is made. In other words, the neurons should signal the planned saccade to (or away from) the choice target in its receptive field (RF). That was immediately confirmed—no surprise, as it was almost guaranteed by targeting LIP. Far Metalloexopeptidase more interesting, however, were the dynamical changes in the neural firing during
the period of random dot viewing. The evolution of this activity occurs in just the right time frame for decision formation (Figure 3). Indeed, the average firing rate in LIP approximates the integration (i.e., accumulation) of the difference between the averaged firing rates of pools of neurons in MT whose RFs overlap the random dot motion stimulus. It is known that the firing rate of MT neurons is approximated by a constant plus a value that is proportional to motion strength in the preferred direction (Britten et al., 1993). For motion in the opposite direction, the response is approximated by a constant minus a value proportional to motion strength. The difference is simply proportional to motion strength. Interestingly, in LIP, the initial rate of rise in the average firing rate is proportional to motion strength (Figure 3C, inset), suggesting that the linking computation is integration with respect to time (Roitman and Shadlen, 2002 and Shadlen and Newsome, 1996). This integration step is supported directly by inserting brief motion “pulses” in the display and demonstrating their lasting effect on the LIP response, choice, and RT (Huk and Shadlen, 2005). Moreover, the signal that is integrated is noisy, giving rise to a neural correlate of both drift and diffusion.