1. 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)

2. 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

3. 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

4. Salinas & Sejnowski, 2001 Gain Modulation In Neurons

5. Gain Fields: Gain Modulation Without Changing RF

6. Gain Fields Response of one neuron The downstream response R –e.g.

7. Gain Modulation in Cognition Coordinate transformations –Modulatory quantity: gaze angle Translation-invariant object recognition and size constancy –Modulatory quantity: attention Motion processing

8. Gain Modulation In Coordinate Transformations: Modulator: Gaze Angle

9. Gain Modulation In Coordinate Transformations

10. Salinas and Abbott, 1996 A Model of Multiplicative Neural Responses in Parietal Cortex Synapse weights for recurrent connections

11. Simulations

12. 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.

13. One Model of Neglect (A Coordinate Frame Syndrome) Pouget & Sejnowski, 2001

16. One Model of Neglect (A Coordinate Frame Syndrome) The unilateral lesion is modeled by deleting the two right maps.

17. Neglect (Contd.)

20. Salinas and Abbott, 1997 Invariant Visual Response From Attentional Gain Field

21. Simulation of Model Network for Images Translated Across Visual Field

22. Salinas and Abbott, 1997 Simulation: Images at Different Scales

23. Chance, Abbott, and Reyes, 2002 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.

24. Changing the Level of Background Input Modulates Gain

25. 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.