Re: Poster 678
On Sun Dec 6, Grover wrote
>Dr. Stuart: Hope you are enjoying the meeting. Great poster.You indicate that the mechanisms that may be responsible for the changes in vibration detection thresholds on the ipsilateral face are unclear and require further investigation. What are the current hypotheses?
Dr Grover: Thanks for your interest and feedback on our poster. Herewith our thoughts -
Although traditionally it has been accepted that the projections from the face are primarily to the contralateral cortex, there are an increasing number of recent reports (eg J.Comp.Neurol., 363,597-607, 1995 & J.Comp. Neurol., 371, 513-521, 1996) that employed microelectrode mapping and anatomical tracing techniques demonstating that in primates a significant proportion (up to 40%) of trigeminal projections to the thalamus and to area 3b are ipsilateral in origin. Speculation on the function of such bilateral representation basically centres on the manipulation of food within cheek pouches of various primate species. Those species that manipulate food in search of seeds would require a high degree of sensory localisation, thus ipsi- and contralateral representations of these intraoral structures would have been evolved. A similar argument may also apply to humans for the sensory information required during speech, especially if one takes into account the vibrotactile nature of sound articulation and therefore the importance of vibrotactile afferent feedback.
We should also note that the assessment of other sensations (temperature and light touch) on the face revealed a deterioration of these modalities contralaterally. Therefore, it appears that there is a modality specific difference in projections from the face to the cortex. Although, bilateral projections for fast adapting afferent units involved in vibrotactile signalling may be the dominant scheme in humans, this still would not explain the dramatic deterioration of vibration sensibility on ONLY the ipsilateral face. One obvious suggestion would be that the projections of this specific modality from the face are predominantly ipsilateral. However, this would only be speculation and that is why further research is required to solve this issue.
Mon Dec 7