sustained delay activity prior to execution of the movement could reflect:
1. motor plan (intention)
2. spatial attention
3. other priority of a target for potential actions
Different brain regions signal intention/attention/priority of spatial targets for
different type of movements.
What are the spatial reference frames in which these neurons represent target locations for future approach?
eye-centered
head centered
body centered
Spatial reference frame:
a set of axis
Consider a FEF cell that fires to trigger saccade in a particular direction
spatial tuning depends on the reference frame of the neuron
describe the memory saccade (memory reach) task
to see whether neurons in area ______ represent the flash (target location) relative to the current position of the eye, hand, or head.
so the peak in the firing rate show which direction the movement was in. And you can tell the coordinate based on that.
If the neural representation of the target is in an eye-centered ref frame then the location of the movement field (relative to head) will
shift with eye position
If the neural representation is in an head-centered ref frame then the location of the movement field (relative to head) will
not shift with eye position (x-axis is head centered location) on top of each other
Other possibilities include:
1. intermediate reference frame (partial shift)
2. eye-centered representation in which response strength varies with eye position (gain field) amplitude changes
many brain areas contain neurons that respond to stimuli delivered though multiple _______________
sensory modalities
The most extensively studied multi-sensory area of the brain is the
superior colliculus (SC)
SC is mainly thought to be involved in generating commands for coordinating
eye and head movements that orient gaze to objects of interest
Neurons in deep layers of SC receive
visual
auditory
somatosensory inputs
Many neurons in SC respond to both visual and auditory stimuli when those stimuli will be targets for an upcoming
eye movement (saccade)
Responses of retinal ganglion cells clearly depend on the location of a visual stimulus
relative to the fovea of the retina.
Auditory signals, by contrast are initially encoded _________________
relative to the head, (but overall use an intermediate reference frame)
Jay and Spark's experiment:
eye centered and head centered coordinates can be distinguished by having a subject fixate at different positions and testing
whether the RF of a neuron moves with the eyes or stays fixed relative to the head.
neurons in LIP discharge prior to making
saccades
neurons in PRR discharge prior to making
arm movements
Neurons in deep layers of SC have spatially
co-registered receptive fields.
As the eyes move, the location of an object in the world centered coordinates also needs to move in order to maintain the same stimulus on the
retina
summary of Jay and Spark's experiment:
they measure horizontal shift of the receptive field (in head centered coords) for each pair of eye positions (-24, 0, 24 deg)
Jay and Spark's experiment found that visual responses are close to
eye centered