Daneault et al. Journal of Medical Case Reports 2011, 5:449 http://www.jmedicalcasereports.com/content/5/1/449 Page 4 of 6 Figure 2 Characteristics of physiological tremor (PT). This graph illustrates the amplitude, median power frequency (MPF) and power dispersion of PT in all four trials. Note that for all characteristics within each trial, all values are representative of the average of a five-second epoch. Solid dots represent values for the left index finger and white dots represent values for the right index finger. Top row: PT amplitude of both index fingers for each trial calculated on the displacement time series comprising oscillations between 1 to 30 Hz. The reference line represents the upper specification of two standard deviations of PT amplitude in 93 healthy young adults taken from a data bank [5]. This indicates that values lying below this reference line are considered within normal ranges, whereas those that lie above are considered abnormal. Middle row: MPF of both index fingers for each trial calculated on the velocity power spectrum comprising oscillations between 1 to 30 Hz. The reference lines represent the upper and lower specifications of two standard deviations of PT MPF in 93 healthy young adults taken from a data bank [5]. This indicates that values lying between those reference lines are considered within normal ranges whereas those that lie outside are considered abnormal. Bottom row: power dispersion (frequency band containing 68% of total power centered at the MPF) of both index fingers for each trial calculated on the velocity power spectrum comprising oscillations between 1 to 30 Hz. The reference lines represent the upper and lower specifications of two standard deviations of PT power dispersion in 93 healthy young adults taken from a data bank [5]. This indicates that values lying between those reference lines are considered within normal ranges whereas those that lie outside are considered abnormal. Of note is that characteristics of the left index finger remain steady throughout all four trials whereas characteristics of the right index finger begin changing as early as in the second trial. PT characteristics between both hands as the seizure approached. This strongly suggests that lateralized des- cending pathways were involved in the changes observed and excludes systemic changes such as increased adre- naline often observed before a seizure. PT is defined as involuntary oscillation of a limb. These oscillations stem from neural activity within the central nervous system and mechanical properties of the limb examined; all of which are modulated by reflex activity (see [10] for a review). It is believed that central oscillations are generated and propagated through a cer- ebello-thalamo-cortical pathway [9], whereas the mechanically-generated oscillations are a function of limb inertia and rigidity [6]. Cortical involvement in PT has long been suspected. For example, we have shown that the resurgence of central components of PT can be prevented after tremor amplitude normalization follow- ing ventrolateral thalamotomy [9]. In these cases, it was suggested that the cerebello-thalamo-cortical pathway involved in PT generation and propagation was simply interrupted. However, it is well known that the ventro- basal thalamic nucleus and not the ventrolateral thala- mic nucleus synapses within the primary somatosensory cortex [11], the localization of epileptic activity in the present case. Rather, the ventrolateral thalamic nucleus synapses within motor and accessory motor areas (see [12] for a review). One simple explanation would be that altered neural activity from the somatosensory cor- tex was transferred to the motor regions via arcuate fibers. The findings from the present case cannot con- clusively characterize the neural mechanisms involved in tremor modification, but these neural pathways are surely involved. Since PT characteristics, whether ampli- tude or spectral, were altered for the right side while they remained relatively steady for the left and the parti- cipant’s abnormal cerebral activity was localized within her left hemisphere, we can conclude that the changes in PT characteristics were caused by this atypical brain activity. Nonetheless, we cannot exclude the possibility that central modulation of reflex activity could have caused the observed changes in PT. The possible involvement of our patient’s frontal het- erotopias on the results presented here is minimal. Indeed, since this condition is chronic whereas epilepti- form activity is intermittent, it would produce long-last- ing alterations to PT properties. As the results clearly demonstrate, PT characteristics in the first trial were normal whereas, starting in the second and culminating in the fourth, those properties were being altered by an abnormal mechanism, namely the epileptic seizure activity. Interestingly, only PT characteristics were significantly altered while other physiological signals, namely EMG, heart rate and respiration, remained unchanged