introduction to the field of behavioral disorders [2, 3]. Gage survived and recovered without any motor or cognitive impairment. However, “he was no longer Gage,” according to his friends [2]. Formerly, a responsible and socially well-adapted individual, he became irreverent and capricious, could not hold a job and died 12 years later under the custody of his family. Harlow published a very comprehensive description of the behavioral changes occurring after Gage’s accident, which included a several-year-long follow-up of the patient and testimony of relatives and friends [2]. He also presumed that these behavioral modifications were associated with lesions to a particular region of the frontal cortex, making it one of the earliest correlations between behavioral disorders and neuroanatomy.
In addition to medical records, behavioral changes have occasionally become the object of public perception through artistic acknowledgment and penal proceedings. Contemporary to Phineas Gage, Eadweard Muybridge, a bookseller established in San Francisco, survived a stagecoach accident in 1860 [6]. Again, this patient recovered physically and intellectually but his personality transformed dramatically. He changed the spelling of his name dozens of times and was even charged with the murder of a man suspected of having an affair with his wife. Yet, this lesion triggered a new artistic expression and re-oriented his career: He became a pioneering photographer and developed the “zoopraxiscope,” a precursor of motion pictures. Based on visual symptoms and the loss of smell and taste, Eadweard Muybridge’s brain lesion is assumed to have occurred in the orbitofrontal cortex.
These 2 case reports of trauma established the relationship between lesions to a specific brain area and acquired behavioral deficits that spared intellectual abilities. A few decades later and with the development of neurosurgical procedures, neuroanatomical correlates became accessible to more specific investigation and further underscored the relevance of behavior assessment. One of the sessions at the 2nd International Neurological Congress in London (1935) was thus dedicated to the functions of the frontal lobe [7], and included the well-documented follow-up of patient Joe A., the first bilateral frontal lobectomy case with long survival [8]. Intellectual performance in this patient was assessed using psychometric testing, whereas behavioral status remained at the descriptive level, relying (as for almost all cases of that era) mainly on the neurologist’s observations and heteroanamnesis. Following the resection, Joe A. became logorrheic, self-absorbed, puerile and distractible, with perseverations and sudden mood changes. Whilst Brickner showed severe deterioration in Joe A.’s behavior after surgery, Hebb and Penfield reported a 27-year-old patient who improved after partial bilateral frontal lobectomy [9, 10]. Following a traumatic brain injury to the frontal poles at the age of 16 years, K. M. suffered from severe epileptic seizures. During interictal states, he was described as “childish, violent, stubborn and destructive” by his relatives and the whole neighborhood. After operation, he became “normal in every way” [9]. The 6-year follow-up showed that he had been independent in his daily life activities and successful in finding jobs since his discharge from the army. Although he frequently changed jobs, he was able to save for the future. Here, K. M.’s post-surgical behavioral improvement was evaluated through information given by his parents and his brother, as well as through the “independent testimony of 3 residents of the village,” namely a taxi driver, a storekeeper, and a waitress.
Two decades later, Luria et al. [11] went a step further and published a seminal detailed experimental analysis about the impairment in behavioral regulation after the removal of part of a left frontal meningioma. Patient Zav underwent a full test battery addressing different modalities (verbal, non-verbal, symbolic instructions) and assessing various levels of behavioral regulation (apprehension of instructions, evaluation of errors). This study also introduced the innovative concept of “orienting reaction,” that is, an autonomic signal based on previously registered feedbacks produced by the outcomes of actions, which is assumed to be disturbed in patient Zav. The recording of vascular and galvanic skin responses (GSR) indeed showed the absence of activation during tasks and reinforced the hypothesis of a lack of error utilization underlying behavioral regulation and decision-making impairments. As described below, this pioneering approach was made popular 30 years later with the “somatic marker hypothesis” [12, 13].
Advances in neurosurgery and the London congress also led to the rise of lobotomy. Initiated by Swiss psychiatrist Gottlieb Burckhardt as early as 1888 and later extensively implemented by Egas Moniz and Walter Freeman, the controversial “psychosurgery” consisted mainly of frontal lobotomy, that is, the (minimal-to-extensive) deletion of the fibers connecting the frontal areas with the rest of the brain, to decrease symptoms of mental illness [14, 15]. Post-surgery patients typically showed apathy, loss of initiative, and a decrease in social interactions. Not only were these behavioral characteristics just outlined and their follow-up was brief, but they were also certainly biased by pre-existing mental disorders.
War Times, Questionnaires, and Group Studies
World War I sadly supplied much data for the understanding of personality changes due to brain trauma [16]. However, World War II triggered more systematic and larger-scale assessments: Interviews and questionnaires with features amenable to quantification and scoring thus resulted in first group studies.
Large cohort studies with patients based on war records were carried out retrospectively. For instance, Lishman examined psychiatric and behavioral disabilities after head injury from the Oxford collection of head injury records, compiled during World War II [17]. A detailed follow-up was available up to 5 years after the acute stage for most patients, much of this material consisting of questionnaires listing a wide range of symptoms. In Lishman’s study, altered behavior was part of the category “psychiatric disability” defined “as disturbance in any area of mental life, as reflected by impaired intellectual function, disorder of affect, disorder of behavior, somatic complaints without demonstrable physical basis, and/or formal psychiatric illness.” Affective disorders consisted of depression (episodic or continuous), emotional lability, morbid anxiety and phobias, irritability, overt aggression, apathy, loss of initiative and euphoria, whereas behavioral disorders involved crime or misdemeanours, sexual disturbance, lack of judgment, reliability, consideration for others, childish or facile behavior, restlessness, impulsiveness, and disinhibition. Likewise, Grafman et al. [18] retrospectively investigated the presence of aggressive and violent behavior in veterans who suffered a penetrating brain injury during their service in Vietnam. Besides an open question asked by the neurologist (“Have you ever had any violent behavior against persons or things? We all lose our temper now and then, but have you ever beaten someone up or torn up a room?”), the veteran and family members completed questionnaires. It included the Beck Depression Inventory [19], the Katz Adjustment Scale (relatives’ judgment of the subject’s competency across a variety of social and behavioral domains) [20],