Contrast sensitivity is enhanced by expansive nonlinear processing in the lateral geniculate nucleus.

Area of Science:

• Neuroscience
• Visual Neuroscience
• Computational Neuroscience

Background:

• Neural responses in the visual pathway are non-linear with stimulus strength.
• Primary visual cortex neurons show expansive and compressive nonlinearities.
• Lateral geniculate nucleus (LGN) neurons exhibit compressive nonlinearity at high contrasts.

Purpose of the Study:

• To investigate the possibility of expansive nonlinearity at low contrasts in LGN neurons.
• To characterize the contrast-response functions of LGN neurons.
• To assess the impact of LGN nonlinearities on visual processing models.

Main Methods:

• Acquired contrast-response data from a population of LGN neurons.
• Fitted best-fit functions to contrast-response data.
• Measured LGN neuron responses to m-sequence white noise.
• Examined the static relationship between linear prediction and actual spike rate.

Main Results:

• Most LGN cells' best-fit functions required an expansive component at low contrasts.
• The static relationship between linear prediction and actual spike rate was well-fit by an expansive nonlinear power law (average exponent of 1.58).
• Demonstrated expansive nonlinear responses in early visual pathway neurons at low contrasts.

Conclusions:

• LGN neurons exhibit expansive nonlinear responses at low contrasts.
• This thalamic expansive nonlinearity has significant implications for visual processing models.
• The findings may affect the interpretation of various visual functions.