Effects of Psychological and Biomechanical Trauma on Brain and Behavior Thomas W. McAllister and Murray B. Stein, Annals of the New York Academy of Sciences Page 1 of 10

Introduction

Traumatic brain injury (TBI) has received much attention as a frequent cause of injury and disability in the current conflicts in Iraq and Afghanistan.¹ Questions have been raised about whether the most common mechanism of TBI in these conflicts, blast concussive injury, results in different neuropsychiatric sequelae than those associated with more conventional contact or inertial forces.^2,3 Some investigators have suggested that the neuropsychiatric sequelae reported in military personnel returning from combat are better explained as the effects of exposure to psychological trauma with resultant depression or stress-related disorders (e.g., posttraumatic stress disorder [PTSD]).^4,5 The Department of Defense has underwritten an aggressive research program to address these questions, and much emphasis has been placed on the need to distinguish the effects of biomechanical and psychological trauma.

Investigators and clinicians new to this field might think that the neuropsychiatric effects of both biomechanical and psychological trauma have only recently been appreciated, but this is not the case.^6–8 In fact, debate about the relative roles of biomechanical and psychological trauma in symptom genesis have been taking place for well over 100 years.^6,9 Within a military context, these discussions first arose with the emergence of “shell shock” in World War I, a term supplanted by “postconcussional syndrome” (or some variation of that phrase) in World War II (see Jones et al.⁶ for discussion). In each instance inordinate attention was placed on parsing out the neurologic/“organic” (biomechanical) contributions from the psychological/“psychoneurotic” contributions, with a reluctance to embrace the possibility that both forms of trauma might operate through overlapping and/or complementary mechanisms.

Older descriptions of military personnel with combat-related distress ring quite true with current clinical experience. For example, Cramer,⁷ in describing the clinical picture of what he termed

“cerebral blast concussion,” wrote in 1949, . . . one or more nearby explosions, causing no overt or external harm to the skull, nevertheless render the subject unconscious. After this, he has a retrograde amnesia for all but the flash of the explosion, and thereafter anterograde amnesia for a variable period. During this time he may have great motor unrest and normal or exaggerated responses to stimuli. On regaining consciousness, he has intense and intractable headache, which later gives way to a milder, but constant, headache; tinnitus; intolerance of noises; tremors, and ‘nervousness’. . . ‘Anxiety’ is manifest, and ‘depression’ and ‘regression’ are often employed to describe the dejection and muteness that characterize the behavior of the victim. Neurologic examination is, for the most part, ‘negative’ . . . the most frequent [symptoms are] the inability to tolerate loud noises or sudden movements; these stimuli sometimes precipitated strong startle responses . . . either spontaneous or in response to stimuli, such as the explosion of a shell or the passage of aircraft (p. 6).

Once again, there was great debate about the relative contributions of psychogenesis and physiogenesis. Lishman, in his study of World War II veterans with brain injury, posited that the initial insult had its basis in neural injury but psychological factors subsequently assumed greater importance in maintaining persistent symptoms, particularly after mild TBI (MTBI).^10–12

Before the Diagnostic and Statistical Manual of Mental Disorders (3rd Edition) (DSM III) adopted the diagnostic category of PTSD, a variety of terms were used to describe behavior attributed to combat-related stress, including acute and chronic combat stress reaction, shell shock, and combat fatigue.¹³ Thus, the interaction of psychological and biological trauma, particularly in a combat or military context, has a rich history that can inform our deliberations today. As a starting point for these considerations, this paper provides an update on what is known about the neuropsychiatric sequelae of biomechanical and psychological trauma, as well as the effects of exposure to both. Clinical implications are also outlined.

Biomechanical aspects of brain injury

There are two broad categories of forces that result in brain injury: (1) contact or impact and (2) inertial acceleration or deceleration. Contact injuries result from the brain coming into contact with an object, which might include the skull or some external object.¹⁴ The configuration of the external surface of the brain, how it is situated in the skull, and the uneven topography of the inner surface of certain skull regions are factors that result in heightened vulnerability to impact forces for certain brain regions.¹⁵ Frequent sites of such injury are the anterior temporal poles, the lateral and inferior temporal cortices, the frontal poles, and the orbital frontal cortices.

From the Annals of the New York Academy of Sciences, October 2010 issue. Used with permission.

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