Impact of realignment on spinal functional MRI time series

Stimulus site and modality dependence of functional activity within the human spinal cord

Chronic pain is thought to arise because of maladaptive changes occurring within the peripheral nervous system and CNS. The transition from acute to chronic pain is known to involve the spinal cord (Woolf and Salter, 2000). Therefore, to investigate altered human spinal cord function and translate results obtained from other species, a noninvasive neuroimaging technique is desirable. We have investigated the functional response in the cervical spinal cord of 18 healthy human subjects (aged 22-40 years) to noxious thermal and non-noxious tactile stimulation of the left and right forearms. Physiological noise, which is a significant source of signal variability in the spinal cord, was accounted for in the general linear model. Group analysis, performed using a mixed-effects model, revealed distinct regions of activity that were dependent on both the side and the type of stimulation. In particular, thermal stimulation on the medial aspect of the wrist produced activity within the C6/C5 segment ipsilateral to the side of stimulation. Similar to data recorded in animals (Fitzgerald, 1982), painful thermal stimuli produced increased ipsilateral and decreased contralateral blood flow, which may reflect, respectively, excitatory and inhibitory processes. Nonpainful punctate stimulation of the thenar eminence provoked more diffuse activity but was still ipsilateral to the side of stimulation. These results present the first noninvasive evidence for a lateralized response to noxious and non-noxious stimuli in the human spinal cord. The development of these techniques opens the path to understanding, at a subject-specific level, central sensitization processes that contribute to chronic pain states.

A low-cost implantable near-infrared imaging system of spinal cord activity in the cat

A low-cost device using diffuse optical imaging (DOI) for measuring in vivo hemodynamic changes in the spinal cord has been developed. The proposed system is aimed at monitoring for the first time real-time hemodynamic changes associated with intraspinal rhythmic motor activity monitored by electroneurogram (ENG) evoked in paralyzed cats (fictive locomotion). The device contains the emitting and collecting probes within a saddle that fits over a vertebra and has been developed with discrete component circuits. Experiments performed in two acutely decerebrate and paralyzed cats confirm a noticeable and reproducible hemodynamic response during episodes of fictive locomotion. The device is designed so that it could be implanted chronically. In the future, a multi-implant imaging platform could measure long-term hemodynamic changes in the spinal cord.