Gain Modulation Huei-Ju Chen Papers: Chance, Abbott, and Reyes(2002) E. Salinas & T. Sejnowski(2001) E. Salinas & L.G. Abbott (1997, 1996) Pouget & T. Sejnowski (2001)
Outline • What is gain modulation? • Gain modulation in the parietal cortex (coordinate transformations) • Gain modulation in Neglect • Invariant visual responses from attentional gain fields • Gain modulation from background synaptic Input
Introduction • Gain modulation is a nonlinear way in which neurons combine information from two or more sources, which may be of sensory, motor, or cognitive origin. • One input affects the gain of the neuron to the other input without modifying the neuron’s receptive field properties. • Salinas and Sejnowski, 2001
Gain Modulation In Neurons Salinas & Sejnowski, 2001
Gain Fields • Response of one neuron • The downstream response R • e.g.
Gain Modulation in Cognition • Coordinate transformations • Modulatory quantity: gaze angle • Translation-invariant object recognition and size constancy • Modulatory quantity: attention • Motion processing
A Model of Multiplicative Neural Responses in Parietal Cortex • Synapse weights for recurrent connections Salinas and Abbott, 1996
One Model of Neglect (A Coordinate Frame Syndrome) • Neglect is a neurologic syndrome characterized by a conspicuous inability to react or respond to stimuli presented in the hemispace contralateral to the lesion.
One Model of Neglect (A Coordinate Frame Syndrome) • Pouget & Sejnowski, 2001
One Model of Neglect (A Coordinate Frame Syndrome) • The unilateral lesion is modeled by deleting the two right maps.
Invariant Visual Response From Attentional Gain Field Salinas and Abbott, 1997
Simulation: Images at Different Scales Salinas and Abbott, 1997
Gain Modulation From Background Synaptic Input • Chance, Abbott, and Reyes, 2002 • By introducing a barrage of excitatory and inhibitory synaptic conductance that mimics conditions encountered in vivo into pyramidal cells in rat cortex, the gain of a neuronal response to excitatory drive are shown to be modulated by varying the level of background synaptic input. Chance, Abbott, and Reyes, 2002
Summary • Gain modulation is a prominent feature of neuronal activity recorded in behaving animals, but the mechanism by which it occurs is still not clear. • Gain modulation is very close to multiplicative. However, its essential feature is nonlinearity. • Gain fields have been implicated in eye and reaching movements, spatial perception, attention, navigation, and object recognition.