Table 1.

A summary of the results and their implications for the biological origin of the optical signal

RESULTS
Question	Protocol	Results	Conclusion
Contribution of Motion	Neuromuscular Block (animal model)	Signals are lost following block and return with washout of the drug	Contractile motion induced by nerve stimulation is necessary and sufficient to generate an intermediate signal
	Surgical Denervation (animal model)	Nerve transection also eliminates the optical signal
	Sensory vs. Mixed Nerves	Sensory Nerves: No Signal Mixed Nerves:    Large Signal
Structures involved	Spectral Dependence	At the time of peak signal amplitude, the spectral nature of the signal reflects that of hemoglobin	Motion of blood-containing structures dominate the signal
	Vascular Occlusion	During occlusion, changes to the Signal are not the same as changes to the background tissue optical properties	Signal is not derived from tissue capillary beds, which determine background optical properties
Dilation or Displacement	Spatial Dependence	Signals are positive-going in some locations and negative-going in others	Displacement of a large vessel could account for the signal, but not dilation, which would cause signals to be either always positive or always negative