Oral Presentation Neuropathophysiology - an ISH satellite 2012

Identification of sites of skin sympathetic outflow during concurrent recordings of sympathetic nerve activity and fMRI (#3)

Cheree James 1 , Vaughan G Macefield 2 , Luke A Henderson 3
  1. University of Western Sydney, Oatley, NSW, Australia
  2. University of Western Sydney, Sydney, NSW, Australia
  3. University of Sydney, Sydney, Australia
BACKGROUND: The use of brain imaging to study the central control of the sympathetic nervous system in human subjects has largely relied on correlating changes in signal intensity with indirect measures of sympathetic outflow. We recently showed that it is possible to use intraneural microelectrodes to record muscle sympathetic nerve activity while performing functional magnetic resonance imaging (fMRI) of the brainstem (Macefield & Henderson, 2010). We have since gone on to identify suprabulbar areas within the brain that may contribute to the generation of spontaneous MSNA and SSNA at rest. METHODS: SSNA was recorded via a tungsten microelectrode in 13 subjects. Gradient echo, echo-planar fMRI was performed using a 3T scanner (Philips Achieva). 200 volumes (46 axial slices, TR=8 s,TE=40 ms, flip angle=90 deg, rawvoxel size =1.5x1.5x2.75 mm) were collected in a 4s-ON, 4s-OFF protocol. Total sympathetic burst amplitudes were measured from the RMS-processed mean voltage amplitude during the 4 s period between scans. Blood Oxygen Level Dependent (BOLD) changes in brain signal intensity (SPM5: random effects, uncorrected p<0.005) were measured during the subsequent 4 s period. RESULTS: Spontaneous SSNA was positively correlated to signal intensity in the right anterior insula, right frontal cortex, right orbitofontal cortex and bilaterally in the mid-cingulate cortex and precuneus. Conversely, the left orbitofrontal cortex and left anterior insula was negatively correlated to signal intensity and skin sympathetic nerve activity. CONCLUSIONS: In conclusion, by performing concurrent microneurography and fMRI we have shown that spontaneous fluctuations in sympathetic nerve activity to skin covaries with activity in several discrete areas within the brain, leading us to conclude that certain cortical areas, such as the precuneus, may provide a “wakefulness drive” to SSNA.