Changes in cerebral blood flow have also been observed as long as three years after a concussion in studies using single photon emission computed tomography (SPECT). At least one study with functional magnetic resonance imaging (fMRI) has shown differences in brain function during tasks involving memory after mild traumatic brain injury (mTBI) although they were not examining PCS specifically.Not all people with PCS have abnormalities on imaging, however, and abnormalities found in studies such as fMRI, PET, and SPECT could result from other comorbid conditions such as depression, chronic pain, or posttraumatic stress disorder (PTSD). Proponents of the view that PCS has a physiological basis point to findings that children demonstrate deficits on standardized tests of cognitive function following a mild TBI. A few studies have shown that people with PCS score lower than controls on neuropsychological tests that measure attention, verbal learning, reasoning, and information processing, but issues related to effort and secondary gain can not be ruled out as contributing to these differences. Recovery as measured by scores on cognitive tests frequently do not correlate with resolution of symptoms; individuals diagnosed with PCS may still report subjective symptoms after their performance on tests of cognitive functioning have returned to normal.
Because PCS symptoms are so varied and many can be associated with a large number of other conditions, doubt exists about whether the term "syndrome" is appropriate for the constellation of symptoms found after concussion. The fact that the persistence of one symptom is not necessarily linked to that of another has similarly led to doubt about whether "syndrome" is the appropriate term.A longstanding controversy surrounding PCS concerns the nature of its etiology – that is, the cause behind it – and the degree to which psychological factors and organic factors involving brain dysfunction are responsible. The debate has been referred to as psychogenesis versus physiogenesis (psychogenesis referring to a psychological origin for the condition, physiogenesis to a physical one). See also
Daniel Amen, post-concussion expert for the National Football League

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