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stimuli restricted to elbow rotation; such neurons appear to be related to joint movement per se, independent of direction. 7. Differences between area 6 and area 4 cells related to elbow movements were barely significant. During active movements, average onset times of cells in areas 6 and 4 were essentially the same. A slightly larger proportion of area 6 cells responded to passive rotation of multiple joints, and during controlled elbow movements they more often exhibited complex response patterns. 8. These results, in conjunction with lesion and stimulation studies, are consistent with a sensory as well as motor role for precentral cortex neurons. Under passive conditions, the responses evoked by joint rotation and cutaneous stimulation may be utilized in perception of such stimuli, particularly in the absence of the more sensitive postcentral cells.

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Do mental images occur in a spatially mapped (i.e., analog, or array-format) representational medium? Kosslyn's (1978) method was used to measure the visual angle of "the mind's eye" to estimate the extent of the imagery medium before and after unilateral occipital lobectomy. It was found that the overall size of the largest possible image was reduced following the surgery. In addition, only the horizontal extent, and not the vertical extent, of the imagery medium was reduced. Finally, it was determined that the S understood the tasks, was not aware of our predictions, and was unaffected by a strong demand characteristic in a different imagery task. These results are consistent with the hypothesis that imagery occurs in a spatially mapped representational medium dependent on occipital cortex.

Migraine-related dizziness (MRD) refers to a disorder in which vestibular symptoms are an integral part of migraine symptomatology. The purpose of this study was to better define the pathophysiology of MRD, which is incompletely understood and to generate hypotheses regarding MRD by assessing the semicircular canal-ocular reflex, the otolith-ocular reflex, visual-vestibular interaction, vestibulo-spinal function, and visually induced postural sway. Subjects included five subjects with MRD, five subjects with migraine without dizziness, and five headache-free controls. Subjects with migraine were tested interictally. Results indicated that the mean gain of the semicircular canal-ocular reflex during both sinusoidal and constant velocity rotation was reduced in subjects with MRD. No changes were noted in the dynamics of the semicircular canal-ocular reflex. The otolith-ocular reflex, assessed with constant velocity OVAR, indicated that subjects with MRD showed a larger modulation component. No group differences were found in the bias component during constant velocity OVAR, nor in semicircular canal-otolith interaction or visual-vestibular interaction. Computerized dynamic posturography indicated that subjects with MRD demonstrated a surface-dependent pattern. Postural sway during optic flow indicated that subjects with MRD swayed more than the other subjects. We hypothesize that competing processes of serotonergic excitation and inhibition alter central vestibular pathways differently for semicircular canal vs. otolithic responses and for vestibulo-ocular vs. vestibulo-spinal pathways.

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Introduction.-Migraine is thought to be genetically complex. There is evidence of an X-linked dominant genetic component. A locus at Xq24-q28 has already been described supporting this hypothesis.Methods.-The X chromosome in 61 migraine families was screened using markers spanning the entire chromosome. Alleles were assigned using the GeneScan Analysis software, analysis for affected relative allele sharing and linkage was performed using Genehunter X and ALLEGRO. For linkage analysis we chose a model based on epidemiological data as well as assumptions drawn on other complex disorders.Results.-Linkage analysis of combined families showed a parametric 2-point logarithm of the odds (LOD) of 2.86 at theta 0.1 between markers DXS8051 and DXS1223, as well as excess allele sharing at marker DXS8051 with a non-parametric LOD score of 2.85.Conclusion.-These results provide suggestive evidence for a susceptibility locus for migraine on Xp22. Families with different types of migraine contributed to this LOD score.

Brief electrical pulses were applied to the pulp of individual pre-molar teeth of 14 healthy, adult volunteers via wire electrodes implanted and sealed in dentine. The sensation threshold was estimated in each individual by the Two-Alternative Forced-Choice Staircase (2AFCS) method. Seven, 5 or 4 stimulus intensities were employed which were equally spaced in a logarithmic scale between 10 microA above threshold and 500 microA. Magnitude estimates of the subjective intensity of the sensation produced by individual dental excitations were obtained. Cerebral tooth pulp-evoked potentials were simultaneously recorded in 11 subjects. The growth of psychological sensory magnitude with increasing strength of electrical stimulus conformed to the general psychophysical power law. Individual power function exponents varied from 0.204 to 0.907 with a mean of 0.475 and a standard deviation of 0.190. The amplitude of TPEPs, measured between components N135 and P293, also was a power function of stimulus intensity. The exponents of individual TPEP amplitude-intensity functions ranged from 0.055 to 0.362 with a mean of 0.144 and a standard deviation of 0.100. These last exponents were substantially smaller than those describing the growth of psychological magnitude estimates. Neither magnitude estimation nor TPEP amplitude-intensity functions displayed abrupt changes in slope which might accompany transition from one operating sensory mechanism to another and/or changes in qualities of subjective sensations from 'innocuous' to 'uncomfortable' to 'painful.' The result of our psychophysical and electrophysiologic experiments indicate that: (1) albeit highly specialized both morphologically and functionally, human tooth pulp has certain fundamental properties in common with other sensory systems and (2) late midline TPEP components may provide measures of central events that, within a range of stimulus intensities, are associated with the perception of pain, but should not be looked upon as specific indicators of pain processes.