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Cortical responses to noxious thermal stimuli depend upon the skin surface area stimulated
ABSTRACTS
Cortical Responses to Noxious Thermal Stimuli Depend upon the Skin Surface Area Stimulated P.A. Geinar 1, N.M. Szeverenyi 2, A.V. Apkarian 1. Depts. Neurosurgery 1 and Radiology 2, SUNY HSC; Syracuse, NY, USA Introduction: Prior functional imaging studies in humans have demonstrated that cortical responses to acute phasic painful stimuli differ from those obtained during chronic painful stimulation. Preliminary studies in humans using functional magnetic resonance imaging (fMR1) have revealed that the differences in the results between the acute and chronic pain studies may be confounded by the different types of noxious stimuli utilized. In this study the cortical responses to three different types of acute phasic noxious thermal stimuli (with a constant stimulus duration) was examined in normal human subjects.
Methods: Normal right-handed subjects were used to investigate cortical activity in the left fronto-parietal cortex. Three different noxious thermal stimuli were utilized, with constant stimulus and control durations (35 seconds each). Noxious stimulus #1: the subject moved the right hand between two different temperature surfaces (65ram diameter): warm (36 ~ and painful (about I~ above pain threshold). Noxious stimulus #2: the subject's right hand was held in constant contact with an annulus (65mm diameter) which consisted of a warm outer ring (14mm wide) and a hot inner core (37mm diameter). The inner core was placed in contact with the individual's hand for the duration of the stimulus and retracted during the control period. Noxious stimulus #3: digit one was maintained in constant contact with a platinum coated resistant temperature device (lmm X 3mm) which alternated between warm and painful temperatures. Each subject underwent two scanning sessions. In each scan session, two types of noxious stimuli were applied to the right hand (#1 and #2 or #1 and #3) and a motor task was performed by the right hand. The motor stimulus consisted of sequentially touching digits two through five to digit one, the control was rest. A 1.5 Tesla MRI system with a within slice voxel size of 1.56 X 1.56 X 6mm, a single surface coil, and an echo planar acquisition sequence were used to image activity changes in 8 slices, for 6 cycles (20 images/slice/cycle were collected). Single voxel T-maps were generated. Regions of interest (ROI) defined by t-values (p>0.05) with significant pixel clusters (p>0.05) were superimposed on anatomic MR images, and statistically tested. Results: Noxious stimuli #1 and #2 resulted in very similar activation maps. The most consistent increased activations were seen in the primary motor (MI), primary somatosensory (SI), secondary somatosensory, anterior cingulate and supplementary motor, poseterior parietal (area 40), and insular cortices. Noxious stimulus #3 exhibited a different cortical response than the other two stimuli with a predominance of decreased activity in most of the cortical areas where increased activity was seen with noxious stimuli #1 and #2 (primarily in MI and SI). The motor task indicated that many of the same areas activated in the noxious stimuli #1 and #2 overlapped with the motor task activation pattern. PsychophysicaUy noxious stimulus #3 consistently resulted in sensitization, while the other two stimuli rarely showed sensitizatrion.
Conclusions: The similarity in activation patterns between noxious stimuli #1 and #2 rule out a significant contribution of hand movement in the activation patterns observed by stimulus #1. The main difference between stimulus #3 and the other two stimuli was the surface area. It should be emphasized that stimulus #3 had a distinct perceptual quality as well. Therefore, the distinct cortical activation pattern for stimulus #3 is related to the surface area, which in turn may be related to the relative proportion of receptor types activated.
$348
Cortical Responses to Noxious Thermal Stimuli Depend upon the Skin Surface Area Stimulated P.A. Geinar 1, N.M. Szeverenyi 2, A.V. Apkarian 1. Depts. Neurosurgery 1 and Radiology 2, SUNY HSC; Syracuse, NY, USA Introduction: Prior functional imaging studies in humans have demonstrated that cortical responses to acute phasic painful stimuli differ from those obtained during chronic painful stimulation. Preliminary studies in humans using functional magnetic resonance imaging (fMR1) have revealed that the differences in the results between the acute and chronic pain studies may be confounded by the different types of noxious stimuli utilized. In this study the cortical responses to three different types of acute phasic noxious thermal stimuli (with a constant stimulus duration) was examined in normal human subjects.
Methods: Normal right-handed subjects were used to investigate cortical activity in the left fronto-parietal cortex. Three different noxious thermal stimuli were utilized, with constant stimulus and control durations (35 seconds each). Noxious stimulus #1: the subject moved the right hand between two different temperature surfaces (65ram diameter): warm (36 ~ and painful (about I~ above pain threshold). Noxious stimulus #2: the subject's right hand was held in constant contact with an annulus (65mm diameter) which consisted of a warm outer ring (14mm wide) and a hot inner core (37mm diameter). The inner core was placed in contact with the individual's hand for the duration of the stimulus and retracted during the control period. Noxious stimulus #3: digit one was maintained in constant contact with a platinum coated resistant temperature device (lmm X 3mm) which alternated between warm and painful temperatures. Each subject underwent two scanning sessions. In each scan session, two types of noxious stimuli were applied to the right hand (#1 and #2 or #1 and #3) and a motor task was performed by the right hand. The motor stimulus consisted of sequentially touching digits two through five to digit one, the control was rest. A 1.5 Tesla MRI system with a within slice voxel size of 1.56 X 1.56 X 6mm, a single surface coil, and an echo planar acquisition sequence were used to image activity changes in 8 slices, for 6 cycles (20 images/slice/cycle were collected). Single voxel T-maps were generated. Regions of interest (ROI) defined by t-values (p>0.05) with significant pixel clusters (p>0.05) were superimposed on anatomic MR images, and statistically tested. Results: Noxious stimuli #1 and #2 resulted in very similar activation maps. The most consistent increased activations were seen in the primary motor (MI), primary somatosensory (SI), secondary somatosensory, anterior cingulate and supplementary motor, poseterior parietal (area 40), and insular cortices. Noxious stimulus #3 exhibited a different cortical response than the other two stimuli with a predominance of decreased activity in most of the cortical areas where increased activity was seen with noxious stimuli #1 and #2 (primarily in MI and SI). The motor task indicated that many of the same areas activated in the noxious stimuli #1 and #2 overlapped with the motor task activation pattern. PsychophysicaUy noxious stimulus #3 consistently resulted in sensitization, while the other two stimuli rarely showed sensitizatrion.
Conclusions: The similarity in activation patterns between noxious stimuli #1 and #2 rule out a significant contribution of hand movement in the activation patterns observed by stimulus #1. The main difference between stimulus #3 and the other two stimuli was the surface area. It should be emphasized that stimulus #3 had a distinct perceptual quality as well. Therefore, the distinct cortical activation pattern for stimulus #3 is related to the surface area, which in turn may be related to the relative proportion of receptor types activated.
$348