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.
| Identifer | oai:union.ndltd.org:PITT/oai:PITTETD:etd-07272008-220819 |
| Date | 08 September 2008 |
| Creators | Bechara, Bernard Philimon |
| Contributors | Marc A. Sommer, Sanjeev G. Shroff, Neeraj J. Gandhi, Douglas J. Weber |
| Publisher | University of Pittsburgh |
| Source Sets | University of Pittsburgh |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.library.pitt.edu/ETD/available/etd-07272008-220819/ |
| Rights | restricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to University of Pittsburgh or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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