The Suppressive Field of Neurons in Lateral Geniculate Nucleus

Abstract

The responses of neurons in lateral geniculate nucleus (LGN) exhibit powerful suppressive phenomena such as contrast saturation, size tuning, and masking. These phenomena cannot be explained by the classical center-surround receptive field and have been ascribed to a variety of mechanisms, including feedback from cortex. We asked whether these phenomena might all be explained by a single mechanism, contrast gain control, which is inherited from retina and possibly strengthened in thalamus. We formalized an intuitive model of retinal contrast gain control that explicitly predicts gain as a function of local contrast. In the model, the output of the receptive field is divided by the output of a suppressive field, which computes the local root-mean-square contrast. The model provides good fits to LGN responses to a variety of stimuli; with a single set of parameters, it captures saturation, size tuning, and masking. It also correctly predicts that responses to small stimuli grow proportionally with contrast: were it not for the suppressive field, LGN responses would be linear. We characterized the suppressive field and found that it is similar in size to the surround of the classical receptive field (which is eight times larger than commonly estimated), it is not selective for stimulus orientation, and it responds to a wide range of frequencies, including very low spatial frequencies and high temporal frequencies. The latter property is hardly consistent with feedback from cortex. These measurements thoroughly describe the visual properties of contrast gain control in LGN and provide a parsimonious explanation for disparate suppressive phenomena.

BOLD and spiking activity

“…1). Given that roughly the same thalamic input is expected on stimulation of either temporal frequency 2 , we conclude that the initial negative oxygen response depended only slightly (10-20%) on thalamocortical synaptic activity and mostly (80-90%) on cortical spiking.…”

Virtual Retina: A biological retina model and simulator, with contrast gain control

“…It is common to the calculations of I C (x, y, t) and I S (x, y, t). K σC ,τC and K σS ,τS are low-pass normalized filters (spatio-temporal integral of one) as presented in equation (1). The surround signal is more low-pass than the center signal, meaning σ S > σ C and τ S > τ C .…”

“…There is evidence that a divisive invariance also exists at the level of the OPL [31,1], probably between horizontal cells and light receptors. We suggest that horizontal cells provide shunting feedbacks to receptor cells in a way similar to that proposed here at the level of amacrine cells.…”

“…On the contrary, the Bonin LGN model [1] proposes the idea of a divisive spatial surround. But it implements an invariance to local luminosity, so it accounts for different effects than our model, that handles contrast gain controls.…”

A common contrast pooling rule for suppression within and between the eyes

“…1B. On the other hand, if isotropic filters were to drive suppression (Hirsch et al, 2002;Bonin et al, 2005), then the mask components would not be processed independently and we might expect the situation as in Fig. 1C.…”