1. A non-invasive method to determine the cerebral hemodynamics in a human subject with depression including, steps of: (a) obtaining a subject's baseline percent carotid stenosis in the extracranial right and left carotid arteries using B-mode and Doppler measurements; (b) obtaining the subject's baseline mean blood flow velocity in cerebral arteries on both sides of the brain using transcranial Doppler ultrasound instrument; (c) comparing the percent carotid stenosis in both right and left to normal limits; (d) simultaneously with (c) determining if the percent carotid stenosis of one side is greater than the other; (e) determining if mean blood flow velocity in the right or left anterior cerebral artery is lower than normal limits; (f) simultaneously with (e) determining if the mean flow velocity of one side of the anterior cerebral artery is greater than the other; (g) simultaneously with (f) determining if there was a right or left anterior cerebral artery hyperperfusion; (h) simultaneously with (g) determining if there was a right or left anterior cerebral artery hypoperfusion; (i) determining if mean blood flow velocity in the right or left posterior cerebral artery are lower than normal limits; (j) simultaneously with (i) determining if mean blood flow velocity of one side of the posterior cerebral artery is greater than the other; (k) simultaneously with (j) determining if there was a right or left posterior cerebral artery hypoperfusion; (l) determining the DSM-IV score using the standard questionnaire; (m) simultaneously with (l) determining if the DSM-IV score was greater than or equal to five; and (n) simultaneously with (m) determining if the cerebral hemodynamic model could be associated with depression.