Trephination [or trepanation] is the oldest known surgical technique. It has been suggested that Stone Age cave dwellers may have treated behavior disorders with [this] surgical method…in which part of the skull was chipped away to provide an opening through which the evil spirit could escape. People may have believed that when the evil spirit left, the person would return to his or her normal state.… Disputes often arise from the interpretation of historical data: a different explanation of trephining is that it was used to remove bone splinters and blood clots resulting from blows to the head in fights between men [Maher, W. B., & Maher, B. A (1985). Psychopathology: I. From ancient times to the eighteenth century. In G. A. Kimble & K. Schlesinger (Eds.), Topics in the history of Psychology (Vol. 2). Hillsdale, NJ: Erlbaum]. This explanation is consistent with findings that most trephined skulls were of men.
Peru has been recognized as a major source of ancient trephined skulls, many of which date back 2300 years.… From a neurosurgical perspective…of the archaeological studies performed on [trephined] skulls,…comparative osteology has shown that almost 70% of patients survived the procedure. The various instruments, hemostatic [blood clotting] agents, anesthetics, surgical techniques, and cranioplasties used are reconstructed from the anthropological literature.… Analysis of the data leads to the conclusion that, despite their rudimentary knowledge of disease, the ancient Incas must have had some knowledge of anatomy and proper surgical procedure.
The anthropological reports of skull trepanation (trephination) among the early Indians of Canada and the United States of America…[indicated] the location of skull perforation was parietal in…[most] cases and less often frontal…or occipital.… The average skull opening was oval or oblong, with a diameter of 3.0 cm. The method of trepanation was probably gradual scraping in most cases. Skull fractures were not present in any case. About 90% of the trepanations showed evidence of healing, indicating survival.
3,800 skulls of inhibitants [sic] of the Baltic Sea coast of previous centuries have been investigated beginning with the neolithic period up to the 18th century. 10 cases of skull trepanation were found, 8 of which were performed in Latvia, 6 were successful. One of them is of large size (120 x 60 mm) and shows traces of healing. It is dated back to the neolithic period. Five were performed before the 18th century. The favourable results testity [sic] the skill and considerable medical knowledge of folk physicians. Furthermore, it also witnesses the great resistance of the organism of ancient people in Latvia in cases of surgical intervention.
[There are also] cases of cranial surgery in direct association with the osseous image of a non trauma induced soft tissue lesion (sinus pericranii).… [A] case, from Alameda, California (Late Middle Period, ca. 300-500 AD), is the earliest and only definitive evidence of invasive surgery from prehistoric North America. Because this individual presents the only bony evidence of cranial surgery other than trepanation or cauterization, it contributes substantially to our extremely limited understanding of medical practices in preliterate societies.
 S. Rifkinson-Mann (Department of Neurosurgery, New York University Medical Center, New York), Cranial surgery in ancient Peru, Neurosurgery, Oct 1988, 23(4).
 David Sue, Derald Sue, & Stanley Sue, Understanding Abnormal Behavior, 4th ed. (Mass.: Houghton Mifflin Co., 1994), p. 18.
 Rifkinson-Mann, Cranial surgery in ancient Peru.
 J. L. Stone & M. L. Miles (Department of Surgery, Cook County Hospital, Chicago, Illinois), Skull trepanation among the early Indians of Canada and the United States, Neurosurgery, June 1990, 26(6).
 V. Derums, Trepanations of the skull in ancient Latvia (author’s transl.), Zentralbl Allg Pathol, 1979, 123(3).
 G. D. Richards (Department of Anthropology, University of California, Berkeley 94720-3712, USA), Brief communication: earliest cranial surgery in North America, American Journal of Physical Anthropology, Oct 1995, 98(2).www.skewsme.com/trepanation.html