section_path: Neurophysiology
section_name: Neurophysiology
paragraph_text: Neurophysiology
  
  Dream study is popular with scientists exploring the mind–brain problem. Some "propose to reduce aspects of dream phenomenology to neurobiology." But current science cannot specify dream physiology in detail. Protocols in most nations restrict human brain research to non-invasive procedures. In the United States, invasive brain procedures with a human subject are allowed only when these are deemed necessary in surgical treatment to address medical needs of the same human subject. Non-invasive measures of brain activity like electroencephalogram (EEG) voltage averaging or cerebral blood flow cannot identify small but influential neuronal populations. Also, fMRI signals are too slow to explain how brains compute in real time.
  
  Scientists researching some brain functions can work around current restrictions by examining animal subjects. As stated by the Society for Neuroscience, "Because no adequate alternatives exist, much of this research must be done on animal subjects." However, since animal dreaming can be only inferred, not confirmed, animal studies yield no hard facts to illuminate the neurophysiology of dreams. Examining human subjects with brain lesions can provide clues, but the lesion method cannot discriminate between the effects of destruction and disconnection and cannot target specific neuronal groups in heterogeneous regions like the brain stem.