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Oculomotor flashcards
Cards in this deck (38)
- 1What are the extraocular muscle fibers found in the 'global' layer, and the 'orbital' layer?Global- singly innervated twitch muscle fibers
Orbital- multiply innervated non-twitch fibers - 2What are the 3 types of saccade?Reflexive, expressive, or voluntary
- 3What is the mathematical relationship between saccade duration and amplitude?Linear
- 4What is the relationship between force needed in a saccade and time and why?Large initial force to generate a motor neuron signal (pulse phase), and then a constant force is required maintaining the new eye position (tonic phase).
- 5What is an anti-saccade?A saccade which occurs in the opposite direction to the suppressed reflex towards a target.
- 6What roles do the frontal eye field (FEF), supplementary eye field (SEF), lateral intraparietal cortex (LIP)?FEF: control voluntary saccades, with a topographical representation of retinal information. Stimulation elicits saccades to reliable locations
SEF: monitors the consequence of eye movements (reward prediction error)
LIP: encodes target info (possibly direction) - 7Who (AY) and how saccades were discovered?Alred Yarbus. Contact lenses with small mirrors, eye movement patterns demonstrated by reflected beams, ballistic eye movements aligned with scene were discovered, dense spots represented by fixation
- 8What are the associated of the nuclei of the (1) lateral rectus muscle (2) superior oblique (3) other extra ocular muscles?1) abducens nucleus
2) contralateral trochlear nucleus
3) oculomotor nucleus - 9Where is saccade amplitude calculated?LMN of the oculomotor nucleus
- 10Where is the direction of saccades determined?In two gaze centres:
- the paramedian pontine reticular formation (horizontal)
- rostral interstitial nucleus (vertical) - 11What is the SC topography organized in accordance with?Auditory and somatosensory information
- 12Describe what the place code is?A sheet where each neuron is maximally responsive to input corresponding to a sensory stimulus at a particular location
- 13Describe the rate code?Frequency of spikes over time.
- 14What is the weighted summation method of converting place codes to rate codes?All neurons are connected to an output neuron, with movement size correlated to weights, proportional to target distance.
- 15What is the neuron diagram, equation and graph of comparing place code to frequency code look like?Should know/check
- 16What is the author/year of 'Converting neural signals from place codes to rate codes'?(Groh, 2001)
- 17What 2 problems does weighted summation encounter?When there are multiple targets the frequency overshoots. The rate code is also affected relative to the target luminance
- 18What methods avoid the problem of multiple selection mechanisms, yet are still affected by luminance?Suppression of all but one: Winner takes all (by lateral inhibition), or a selection mechanism
- 19What mechanism solves both problems of weighted summation? How could this be biologically implemented?Normalization. A denominator channel where an efferent activity copy is sent to a single neuron which sums and appropriately wights input to output cell?
- 20What is the formula, neuronal map, and graph for weighted averaging?output=sum ( weight x activity )/
sum( activity)
Should know/check the rest - 21What 2 problems does weighted averaging encounter?-the denominator channel has to be single cell to allow robust division
-the dynamic range of denominator neuron has to be huge due to fine discrimination relative to large numbers - 22Explain summation with saturation.A truncation in activity according the overall level of activation is implemented. An integrator adds up activity in sheets overtime. Once a threshold is reached all the numerator channel output are blocked, leaving only the integrated signal
- 23Draw the neural map, and graph of place code against rate code.Should know!
- 24Why does the output saturate sooner with more stimuli?Multiple sources mean that the required number of spikes is reached sooner.
- 25How could normalization be achieved in the place coded sheet? What evidence suggests this is not the case?Lateral inhibition (sum(w_i (a/sum a_i)).
FEF & SC can be stimulated in 2 different location, and still produce an average saccade. - 26Why is there a need for summation with saturation?Division is troublesome
- 27What does a blink perturbed path change?Eye velocity
Saccade duration
Trajectories
Mean and average firing rates
Burst duration of SC cells - 28Is the cumulative number, or the distribution, of spikes between blink and normal saccades altered?The distribution is altered
- 29If blink related activity causes increased inhibition in the SC, what affect does this have on the time taken to accumulate the required number of spikes?It takes longer!
- 30What is the main idea posited by the paper 'Dynamic ensemble coding of saccades in the monkey SC'?Dynamic vector summation: Every spike from every cell in SC contributes a tiny movement command.
- 31Write, and explain the formula defining the trajectory of an eye movement, based on tiny contributions from every cell.grad(E(t))=sum_allcells(
sum_allspikesofacell(
eyemovementvector
X diracdeltafunction(t-t_i,k))) - 32How many ways are there to make the same trajectory from tiny movement commands?Many
- 33What does grad(E) movement vector end up resembling?Cumulative spike count
- 34What are the authors and date of 'Dynamic ensemble coding of saccades in monkey SC'?Goosens & Van Opstal, 2005
- 35How did Goosen and Van Opstal validate their model?They used data from 139 monkey SC neurons as input to their model
- 36How did Goosens and Van Opstal reverse predict SC activation to create observed saccades?Having chosen 1 cell with preferred amplitude and direction, they fix the direction and vary the amplitude, and vice versa. Predicted spike counts correlate well with normal and blink perturbed saccades.
- 37What is the problem with vector-averaging in modelling the spatial-temporal transformation of saccades?It does not account for the 'stretching of horizontal and vertical saccade components needed to obtain straight saccades.
- 38Who are the authors (& date) of 'A model of the saccade-generating system that accounts for trajectory variations produced by competing visual stimuli'?Arai and Keller, 2004
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- Exam Neuroscience Flashcards on Oculomotor flashcards, created by samsden on 21/05/2016.
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