This stimulus elicits a profile of LGN activity that is strongly enhanced by adaptation (Figure 3B). buy Lonafarnib Now consider

a V1 neuron that summates LGN inputs with weights that peak for LGN neurons preferring −3° (Figure 3C). As is typical for V1 neurons, the output of this sum is then passed through a stage of divisive normalization (Carandini and Heeger, 2012) and a static nonlinearity (Priebe and Ferster, 2008), neither of which depends on spatial position (Figure 3D). This model V1 neuron exhibits rather different tuning curves depending on the adaptation condition (Figure 3E). In response to balanced sequences, the tuning curve is centered on −3° and therefore resembles the weighting function (Figure 3E, blue). In response to biased sequences, instead, the tuning curve is shifted away (Figure 3E, red). This example illustrates how the tuning curves of model V1 neurons are repelled by the adaptor even though adaptation does not affect the summation weights. Normalization and the static nonlinearity play no role and are present in the model simply to explain

response amplitudes. Normalization, in particular, divides the output of all V1 neurons to all stimuli in the sequence by a common factor k ( Figure 3D). This factor happens to be somewhat larger in the biased condition ( Figure S3), but it cannot change the resulting tuning curves. Rather, the tuning curves of model V1 neurons are repelled because their inputs from remote LGN neurons are disproportionately enhanced. To understand Chlormezanone this summation model further, it helps selleck compound to cast it in terms of matrix operations (Figure 4). The model operates on matrices of LGN responses expressed as a function of neuronal preference and of stimulus position. In the balanced condition, this response matrix is simply diagonal (Figure 4A): the responses of each LGN neuron depend only on the distance between stimulus position and preferred position. We obtain this response matrix by assuming that LGN neurons tile

visual space and have identical tuning width (FWHH ∼10.6°, the median value in our population). In the biased condition, we modify this response matrix by changing the gain of the LGN neurons depending on their preferred position relative to the adaptor (Figure 4B). We obtain the new gain values from the fit to the LGN data (Figure 2C). The responses of model V1 neurons are then obtained by multiplying the matrix of LGN responsiveness by a matrix of summation weights, which describe the tuning of V1 neurons over their geniculate inputs. Extended to the full V1 population, the summation profile becomes a diagonal matrix, whose values depend on the strength and breadth of the convergence from LGN to V1. We assume that this matrix is not affected by adaptation (Figure 4C). Once we found the optimal parameters of the summation profile, we used them to predict the matrices of responsiveness observed in V1 (Figures 4D and 4E). The best-fitting exponential was ∼1.