Introduction

Trepanation is a worldwide ancient practice which refers to the perforation on the skull. It was first discovered and identified by Paul Broca and Ephraim George Squier in the 1860s (Broca 1867a, 1867b; Clower and Finger 2001; Finger and Fernando 2001; Arnott et al. 2003; Verano and Finger 2010). It has been practiced throughout human history from the Neolithic period to the modern era. Moreover, trepanation has been found all over the world, such as in Europe (Piggott 1940; Mariani-Costantini et al. 2000; Facchini et al. 2003; Weber and Wahl 2006; Lopez et al. 2011; Nicklisch et al. 2018; Tulumello et al. 2018; Pasini et al. 2019; Piombino-Mascali et al. 2019), Asia (Zias and Pomeranz 1992; Sankhyan and Weber 2001; Bazarsad 2003; Han and Chen 2007; Han et al. 2007; Lv et al. 2013; Khudaverdyan 2016; Zhang et al. 1918; Popham 1954; Lisowski 1967; Campillo 1984; Rifkinson-Mann 1988; Piek et al. 1999; Weber and Czarnetzki 2001).

Currently, in China, over 100 cases related to ante-/postmortem trepanation have been reported in ** or cutting. Neither fracture nor apparent healing signs are observed on the margins (Fig. 3). Based on the CT scan, a three-dimensional reconstruction shows that the perforation is located in the middle and posterior part of the superior sagittal sinus and cranial inner table beveling could be observed around the perforation. CT images show that there is no highly radiolucent bone reconstruction at the margins, demonstrating that no formation of new bone occurred (Fig. 4). Considering that the tomb is undisturbed based on the original burial and the normal anatomical position of the skeleton, we can conclude that trepanation is probably performed immediately before or after the death of the individual.

Table 1 Measurements of the perforation on the occipital bone (unit: mm)
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Fig. 3
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a Posterior view of the trepanned skull; b closeup of the perforation; c the smooth margin of the perforation with no apparent cut mark; d no bone defect around the perforation

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Fig. 4
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CT reconstruction of the skull (ectocranial and endocranial view of the cranium)

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Discussions

Differential diagnosis

The perforation on the skull could be attributed to several reasons (Aufderheide et al. 1998; Steinbock 1976; Kaufman et al. 1997; Ortner 2003; Petrone et al. 2015; Verano 2016b). Trauma, pathological defect, and postmortem damage could lead to the perforations on the skull which could be mistaken for trepanation. Comminuted fractures caused by blunt force injuries and penetrating injuries are common types of skeletal trauma that are easily confused with trepanation in archeological contexts. Comminuted fractures are caused by low-velocity blunt implements and characterized by multiple fragments with irregular rims and fracture lines (Verano 2016a). Penetrating injuries are the result of the high-velocity projectile implements which typically leave characteristic entrance and exit wounds on the bone (Verano 2016a). The shape and size of the wound are consistent with use of weapons with sharp edges, radial fracture lines, and internal beveling at the entry. Pathological defects with lytic lesions, destructive and irregular margins caused by cranial dysostosis, pyogenic bacteria, tuberculosis, treponemal disease, metastatic carcinoma, multiple myeloma, and bone neoplasm could be misdiagnosed as trepanations as well (Kaufman et al. 1997; Ortner 2003). Postmortem damage to the crania can be created by the breakage, erosion, weathering, and gnawing marks by carnivores and rodents (Verano 2016a).

In the current case, neither fragmental deformation nor radial fractures are observed around the occipital perforation, which is not consistent with the characteristics of trauma. In some circumstances, such kind of perforation without fracture line on the occipital could be formed by using a hard, sharp, and pointed implement at a high velocity (Smith et al. 2015; Forsom and Smith 2017; Jordana et al. 2009). However, in the Neolithic China, only small sharpened stone tools with limited penetrative ability have been unearthed so far (Fig. 5). Due to the location and the thickness of the occipital bone, it is usually difficult to penetrate the cranium in one attempt without causing visible damages to the surrounding bones with such stone tools. The clearly defined edge without any lytic lesion or destructive margin differentiates it from being due to pathological defects or postmortem damages. All this evidence indicates that the perforation on the occipital was created by intentional trepanation.

Fig. 5
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a Experimental simulation of the trepanation on the maxillary of the pig skull; b sharpened stone tool found at Shuanghuaishu site; c endocranial view of the experimental trepanation on the pig skull

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Method and tool of the trepanation

Based on prior studies on trepanation, it is generally categorized into five commonly used techniques when conducting the practice (Campillo 1984; Arnot et al. 2003). (1) Drilling refers to drilling with a hard sharp stone or implement to produce a perforation with neat edges. The size of the perforation depends on the sharpness and the size of the implement used. (2) Grooving refers to the circumscribing of a circular or oval portion of bone from the tables of the skull by repeated cutting with an incisive instrument until a disc of bone can be removed. In common cases, obvious marks left by the sharp implement can be observed on the edges of the perforation. (3) Scra** refers to the abrasing of the outer table, diploe, and the inner table by a hard abrasive implement until the meninges are exposed. The perforation caused by this method can be identified by a slight slope surrounding it, alongside an incomplete and powdery bone that is scraped off. (4) Intersecting linear cutting, also known as the “Indian canoe” style, refers to the cutting of four intersecting straight lines into the plate and the subsequent removal of the middle square piece. It is first found in Peru and is very popular in South America. (5) Boring and cutting refer to drilling of a circle of tightly connected small holes. Subsequently, cutting the bone bridges between them allows the removal of a disc of bone. This method will leave the plate in a slightly gear shape, and only one example is found in the Chaiwobu cemetery in ** is the most common method practiced in prehistoric times, while the cases related to linear cutting and boring and cutting techniques are extremely rare (Lisowski 1967; Campillo 2007). However, it should be noted that in trepanations with well-healed bones, the specific marks left behind may be obscured by bone remodeling on the edges of the perforation (Lastres and Cabieses 1960). However, no consensus has been reached yet regarding the implements used in the practice of trepanation. From the Neolithic period to the modern era, the implement varies in different regions, periods, and cultural contexts.

On the current trepanned skull, although considering the taphonomic effect on the bone, neither cut marks by sharp objects nor a slope by scra** is observed around the perforation. The perforation is oval in shape, which differentiates it from the regular circle created by grooving or linear marks by cutting. To further reconstruct the method of trepanation, the skull of a domestic pig is selected to simulate the trepanning process. Since only tools made of stone and bone are used in the Neolithic China, sharp flints or sharpened animal bones and antlers are believed to be used for drilling and cutting. In the experiment, trepanation is conducted on the maxillary of the pig skull by using a tool with a V-shaped blade to drill and polish the edges of the perforation. A regular circle could be obtained by using a symmetrical V-shaped tool, while an oval perforation which is similar to the one on the human skull is obtained by using an asymmetrical V-shaped tool (Fig. 5). Therefore, it is assumed that the oval perforation on the skull could be drilled by a primitive stone tool with an asymmetrical V-shaped blade (Fig. 6).

Fig. 6
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Schematic diagram of the simulated perforation process

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The motivation of the trepanation

The motivations behind the trepanation are diverse, such as for therapeutic, cultural, and symbolical purposes (Aufderheide et al. 1998). To begin, trepanation for medical purposes aim to treat the trauma on the head or some refractory head diseases caused by mastoiditis, meningioma, osteomyelitis, epilepsy, mental disorder, intracranial tumor, and leprosy (Jørgensen 1988; Smrčka et al. 2003; Andrushko and Verano 2008; Khudaverdyan 2011; Petrone et al. 2015; Facchini et al. 2003; Verano 2003; Erdal and Erdal 2011; Zhang 2018). For example, trepanations accompanied with trauma on the head are found in many regions as a treatment to relieve intracranial pressure from extradural hemorrhage that is caused by an external force (Petrone et al. 2015; Zhang et al. 1965; Jordanov et al. 1988; Ramseier et al. 2005; Gresky et al. 2016). In some prehistoric tribes with worship of skulls, skulls are even trepanned and hung for ritual purposes (Liu 1999). In the Altai stone burials and the Saka population who lives in the steppe of middle Asia, trepanation is performed to extract the brain and to preserve the body (Liu 1999).

To determine the motivation of trepanation, it is essential to distinguish whether the perforation is performed ante-mortem, peri-mortem, or postmortem. A perforation without signs of healing indicates that it could have been performed peri-mortem or postmortem. In the current case, the perforation is observed in a special location of the skull, without any cut marks or signs of polishing, fracture, or pathological conditions. It is located right on the posterior and superior section of the superior sagittal sinus vein, which is precisely in the middle (Fig. 7). The superior sagittal sinus is connected to the important venous reflux of the external part of the brain, which is fatal when damaged. In view of this, two motivations could be hypothesized. One hypothesis is that this trepanation was performed for medical treatment when the individual is still alive. The trepanation is performed on the wound to relieve hematoma but failed due to the unusual and dangerous location of the trepanation. Another hypothesis is that it could be a postmortem ritual practice. There is no solid evidence to support it being a symbolic trepanation, especially when it is a single case among nearly 300 sets of skeletons unearthed from the cemetery. However, we should not exclude the possibility of it having a ritualistic or magical motivation. The trepanation could have been performed on the special location for a particular ritualistic purpose.

Fig. 7
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Illustration of the sagittal sinus. a Head anatomy along the sagittal plane. b CT reconstruction of the endocranial situation

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Conclusion

Though there are abundant researches on ancient trepanation, the origins and distribution of the practice are still a controversial issue. The Neolithic trepanation found in the Shuanghuaishu site is one of the earliest cases along the Yellow River Basin in central China. Multidisciplinary analyses reveal that the perforation on the occipital bone is a result of intentional trepanation, as it is without any signs of cut marks or healing. Archeological evidence and simulated experiment indicate that the trepanation could be conducted by drilling the cranial bone plate with a V-bladed stone tool. In light of the location of the perforation and the limited details on the edges, the motivations behind the practice could be related to medical treatment of the trauma on the occipital bone or a postmortem ritual. More individuals with trepanation might have been discovered in the cemetery, if not for the poor preservation of skeletons in that particular environment. Nevertheless, this research not only significantly provides one of the earliest evidence of trepanation in China but also contributes to further illuminate the origin and distribution of this ancient practice in China.