Survivors of a severe TBI frequently may suffer from deficits of long-term episodic memory, slowed information processing, and deficits of attention, working memory, and executive functions [4]. For example, Masson et al. [5] showed that 5 years after a severe TBI, 44.4% of survivors had a Moderate Disability, and 14.4% a Severe Disability, mainly due to cognitive impairments. Cognitive impairments are frequently associated with behavioral and personality changes [6], poor self-awareness [7] and mental fatigue [8, 9]. Brooks and colleagues [10] reported that, 1 year after the accident, 60% of relatives answered that the patient was “not the same as before,” and this proportion increased up to 74% at 5 years.
Long-term memory
After emerging from coma and the vegetative state, TBI patients usually pass through a phase of global cognitive disturbance, termed posttraumatic amnesia (PTA), characterized by confusion, disorientation for time and place, inability to store and retrieve new information, and some degree of retrograde amnesia [11]. The consistent return to continuous memory indicates clearing of PTA, but memory problems frequently persist. Indeed, memory deficit is one of the most frequent complaints from patients and their relatives after a severe TBI [12]. Brooks et al. [10] found that memory problems were reported by 67% of relatives 1 and 5 years after a severe TBI. Memory failures were the second most frequent relatives’ complaints 5 years postinjury, just after behavioral modifications.
Many studies have shown that patients with TBI suffer from a deficit in the ability to acquire new information (for a recent review see Vakil [13]). Patients perform poorer than controls on all types of memory tasks, whatever the task demand or the nature of the material to be remembered (verbal or visual) [14].The underlying cognitive mechanisms are still debated [13]. Experimental studies suggest that TBI is associated with a slower, inconsistent, and disorganized learning rate [15, 16], an accelerated forgetting rate [17, 18], a higher number of intrusions in free recall, and a reduced ability to spontaneously use active or effortful semantic encoding or mental imagery to improve learning efficiency [19]. In many aspects, memory impairments after TBI seem closely related to attentional and executive impairments, and resemble the kind of memory disorders found after frontal lobe lesion.
In addition, a high prevalence of retrograde memory deficits has been reported after TBI, encompassing both the domains of autobiographical and public events memories and also early acquired basic and cultural knowledge [20, 21].
Working memory
Working memory is a system for both storage and manipulation of information, hence playing a central role in complex cognitive abilities [22]. It is assumed to be divided into three subsystems [22]. The central executive is an attentional control system, while the phonological loop and the visuospatial sketchpad are two modality-specific slave systems, responsible for storage and rehearsal of verbal and visuospatial information, respectively. Although the two modality-specific slave systems are relatively well preserved after TBI, central executive aspects of working memory (particularly the ability to simultaneously store and process complex information or to monitor and update information) seem to be impaired [23].
Attention and speed of processing
One of the most popular models [24] assumes that attention can be subdivided into two broad domains, intensity (the ability to modulate the level of attention on a given task) and selectivity (the ability to select relevant stimuli in the environment). Each of these two domains can be again divided in two components. Within the intensity domain, phasic alterness refers to the ability to respond faster when a stimulus is preceded by a warning signal, while sustained attention refers to the ability to maintain a stable level of performance during a monotonous long-duration task. Within the selectivity domain, focused attention refers to the ability to focus on a relevant stimulus, and hence to discard irrelevant, distracting stimuli, while divided attention refers to the concurrent performance of two competing tasks at the same time.
Mental slowness is one of the most robust findings after severe TBI and may compromise all aspects of attentional functioning. Whether attentional functions are additionally impaired remains debated. Experimental studies suggested that there is little if any specific impairment of phasic alterness, sustained attention, and focused attention beyond slowed processing [25]. However, several studies found a specific impairment of divided attention that depends on the nature and complexity of the task [26–29]. As suggested in a meta-analysis, TBI patients did not differ from controls when the divided attention tasks could be performed relatively automatically, while they were impaired relative to controls on tasks including substantial working memory load [30].
Mental fatigue is a frequent complaint after TBI, and seems closely related to attention deficits. According to Van Zomeren et al. [31], fatigue could be due to the constant compensatory effort required to reach an adequate level of performance in everyday life, despite cognitive deficits and slowed processing. This is known as the coping hypothesis, which has received support from recent experimental studies [9, 32, 33].
Deficits of executive functions
Executive functions are the cognitive abilities involved in programming, regulation, and verification of novel and/or goal-directed behavior [34]. Survivors from a traumatic coma frequently show dramatic personality and behavioral changes. These changes may be related to lack of control (disinhibition, impulsivity, irritability, hyperactivity, aggressiveness) or lack of drive (apathy, reduced initiative, poor motivation) [6]. These modifications are frequently associated with lack of awareness (anosognosia) [7].
From a cognitive perspective, impairments in planning, conceptualization, set shifting, mental flexibility, generation of new information, and inhibition have been documented, although objective assessment of these functions is difficult, due to a lack of sensitivity of most commonly used neuropsychological tasks. Several studies outlined the necessity to use ecologically valid assessment measures of executive functions [35–37].
Global intellectual efficiency
Measures of global intellectual functioning are frequently used in the neuropsychological assessment of patients with TBI [38]. The most widely used instrument is the Wechsler Adult Intelligence Scale, which has the advantage of extensive normative data, permitting statistical comparisons. Patients with severe TBI usually show a pattern of global intellectual decline. However, some measures and indexes are more sensitive to TBI. A discrepancy between verbal and performance IQ has been repeatedly reported, the lower performance IQ being related to slowed visuomotor processing. Similarly, processing speed or working memory indexes are particularly sensitive to TBI, while other subtests, such as verbal comprehension or perceptual organization, appear more resistant to brain injury [39].
ICU care: surgical and medical management—systemic treatment
Out-of-hospital management in traumatic brain injury
Emergency department evaluation of mild traumatic brain injury
Neuroimaging in traumatic brain injury
Follow-up and community integration of mild traumatic brain injury
ICU care: surgical and medical management—neurological monitoring and treatment
