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Ocular Counter Rotation During Gaze Shifts

Bechara, Bernard Philimon (2008) Ocular Counter Rotation During Gaze Shifts. Master's Thesis, University of Pittsburgh. (Unpublished)

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Abducens motor neurons (ABD) are known to receive oculomotor signals via the excitatory and inhibitory burst neurons (BN) as well as head velocity related signals via the vestibular nucleus (VN). If the oculomotor input to the ABD was the same, would there be a difference in the properties of the observed eye movement between head restrained (HR) and head unrestrained (HU) gaze shifts? To answer this question, the activity of 22 BN was recorded during HR and HU visual motor tasks performed by non human primates. A template matching algorithm was used to find a pair of trials (HR, HU) with matching BN activity. This guaranteed that the oculomotor input to the ABD was the same. Matched trials were found to have similar gaze amplitudes, but the peak eye velocity of HU movement was lower than HR movement. A time varying gain of the head velocity input was calculated as the ratio of the difference between the eye velocities over the head velocity. This yielded a gain that was high at the onset of the movement, decreased through out the gaze shift and plateau at one after gaze shift offset. Thus the head movement was highly inhibiting the eye movement at HU gaze onset which decreased throughout the gaze shift until it reached and remained at one at the end of the gaze shift. Finally a computer simulation was used to check if the difference in the eye velocities could be explained by VN inputs. The simulation modeled the difference in ABD firing rate (ÄABD) between HR and HU matched trials as the weighted sum of the difference in the firing rate of VN (ÄPVPc, ÄPVPi and ÄEHc) input. The BN input was not used in this model because for matched trials the input was the same, thus the difference was equal to zero. The simulation showed that the weight of EHc cells input was the highest, thus accounting for most of the difference in the ABD. This lead to the conclusion that EHc cells played a major role in reducing the eye velocity during head unrestrained gaze shifts.


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Item Type: University of Pittsburgh ETD
Status: Unpublished
CreatorsEmailPitt UsernameORCID
Bechara, Bernard
ETD Committee:
TitleMemberEmail AddressPitt UsernameORCID
Committee ChairGandhi, Neeraj Jneg8@pitt.eduNEG8
Committee MemberWeber, Douglas Jdjw50@pitt.eduDJW50
Committee MemberSommer, Marc
Committee MemberShroff, Sanjeev Gsshroff@pitt.eduSSHROFF
Date: 8 September 2008
Date Type: Completion
Defense Date: 8 April 2008
Approval Date: 8 September 2008
Submission Date: 27 July 2008
Access Restriction: 5 year -- Restrict access to University of Pittsburgh for a period of 5 years.
Institution: University of Pittsburgh
Schools and Programs: Swanson School of Engineering > Bioengineering
Degree: MSBeng - Master of Science in Bioengineering
Thesis Type: Master's Thesis
Refereed: Yes
Uncontrolled Keywords: gaze shifts; neural reccording; oculomotor system; template matching; vestibuloocular reflex
Other ID:, etd-07272008-220819
Date Deposited: 10 Nov 2011 19:54
Last Modified: 15 Nov 2016 13:47


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