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A neural test bed for simulating executive control deficits in saccade generation

A neural test bed for simulating executive control deficits in saccade generation. Uday Jagadisan Neeraj Gandhi University of Pittsburgh. Sensorimotor function – a balance hypothesis. Typical oculomotor behaviour displays an alternating pattern of gaze shifts and fixations

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A neural test bed for simulating executive control deficits in saccade generation

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  1. A neural test bed for simulating executive control deficits in saccade generation UdayJagadisan Neeraj Gandhi University of Pittsburgh

  2. Sensorimotor function – a balance hypothesis • Typical oculomotorbehaviour displays an alternating pattern of gaze shifts and fixations • Balanced exchange of activity in the brain between inhibitory networks that maintain fixation and excitatory networks that generate gaze shifts • Balance shift towards increased inhibition difficulty or delay in initiating movements • Balance shift towards increased excitation lack of movement suppression (behaviour as seen in disorders such as ADHD, Schizophrenia)

  3. Model - Reciprocal inhibition in the superior colliculus (SC) (illustration from Munoz & Fecteau, 2002)

  4. Biasing the rostro-caudal balance in SC • Objective: Perturb the balance between rostral SC and caudal SC on a trial-by-trial basis while recording activity in both networks • cannot use microstimulation (difficult to stimulate and record in the same place) • cannot use inactivation (recovery over long time-scales) • Can we use the blink reflex to our advantage? • Omnipause neurons (OPNs) in the PPRF have been shown to shut off during blinks, linked to loopy eye movement associated with blink • Like the OPNs, cells in the rostral SC show a reduction in activity related to saccades – can they also be turned off using blinks? • If so, what are the consequences of this on the caudal network? Schultz, et al. (2010)

  5. Experimental Methods • Single units in rostral and caudal SC (intermediate layers) of monkey (macacamulatta) • Delayed saccade (overlap  500-1200 ms) paradigm • Air-puff delivered at random time on ~25% of trials; analysis focuses on blinks during initial fixation (Fixation Blinks) • Saccade target – IN or OUT of response field

  6. Experimental Methods • Single units in rostral and caudal SC (intermediate layers) of monkey (macacamulatta) • Delayed saccade (overlap  500-1200 ms) paradigm • Air-puff delivered at random time on ~25% of trials; analysis focuses on blinks during initial fixation (Fixation Blinks) • Saccade target – IN or OUT of response field For more on these trials, please visit my poster on Monday afternoon (QQ13 489.01)

  7. Activity in the rostral SC – control vs fixation blink Suppression lasts past the blink into the delay period … … even as the eyes are stable.

  8. Activity in the rostral SC – Summary (4 neurons) Significant

  9. Activity in the rostral SC – Summary (4 neurons) Significant

  10. Activity in the caudal SC – visual and delay activity Increased activity in the visual response

  11. Activity in the caudal SC – visual and delay activity Periods of increased activity

  12. Activity in the caudal SC – saccade-related burst

  13. Activity in the caudal SC – Summary (17 neurons, 2 monkeys)

  14. Activity in the caudal SC – Summary (17 neurons, 2 monkeys)

  15. Behaviour– early (delay period) saccades What happens on these trials? Story so far ...

  16. Increased excitability associated with early saccades

  17. Increased excitability associated with early saccades

  18. Summary • Blinks during fixation lead to reduced fixation network activity that persists for several hundred milliseconds even as the eye position is stable • The reduction of fixation network activity in the rostral SC may be related to the increased excitability in the response of neurons in caudal SC • We have established a model that can be used to study the balance between excitation and inhibition in the saccadic system

  19. Acknowledgements • Thanks to • LabSupport • Neeraj Gandhi • HusamKatnani NIH Grant EY015485 • Gloria Foster • Joe McFerron

  20. Thank you!

  21. Activity during “early” saccades

  22. Increased activity in SC location opposite to target

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