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George E. Carvell, PhD, PT   University of Pittsburgh
 
IMAGING STUDIES IN HUMAN SUBJECTS: INTERPRETATION CAUTION!!
Human Brain Imaging Studies provide an indirect measure of local brain activity or tissue perfusion.

Actual changes in neuronal discharge can only be inferred by the change in metabolic demand that is indirectly measured by the imaging techniques.

Moment by moment alterations in synaptic potentials, membrane potentials and action potentials cannot be 'seen' by current imaging techniques in human subjects.

'Lighting up' a brain area does not necessarily indicate a greater level of excitatory activity. Typically, the cells that have the greatest metabolic demand are inhibitory neurons that influence local circuits in the cortex or in deeper gray structures, e.g., basal ganglia and cerebellum.
= INHIBITORY NEURONS (GAD+)
= EXCITATORY NEURONS (GAD-)
J.S. McCasland and L.S. Hibbard, GABAergic Neurons in Barrel Cortex Show Strong, Whisker-Dependent Metabolic Activation During Normal Behavior. J Neurosci 17: 5509-5527, 1997.
Fig 10,
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Fig 13,
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