Thanks to numerous works in cognitive neuropsychology for over 30 years, consensual views and models of memory functioning have emerged. It is believed that memory is not a unitary system, but that it is composed of multiple independent systems nonetheless working in a relative interactive manner. A classical and well-accepted distinction is the one made between short-term/working memory and long-term memory. The former is involved in the temporary maintenance of information and its mental manipulation [10]. Numerous activities of daily life are constrained by the proper functioning of this memory. This can range from basic activities such as keeping in mind a telephone number to more complex cognitive tasks such as comprehension during reading, mental calculation, problem solving. Long-term memory is divided in two non-completely segregated subsystems [11]. It includes semantic and episodic memories. The former is highly involved in accessing the meaning of words, objects, people and facts but also in the apprehension of the whole world. The latter has an essential role in encoding and storing new information in a spatial and temporal given context. It is the basis on which our autobiographic memory (personal facts) is built.

Attentional system is rooted in a long tradition in neuropsychology. It has been the subject of extensive experimental investigations during the last century. However, the term ‘attention’ remains difficult to define because it involves several phenomena. Numerous cognitive or anatomo-functional models have been proposed in the past. The more consensual in clinical neuropsychology is perhaps the model by Van Zomeren & Brouwer [12]. According to these authors, the attention system is characterized by two axes, which are themselves partitioned into two subcomponents. The first axe corresponds to attention intensity. It covers the notion of attentional arousal, vigilance and sustained attention. The second, the selectivity axe, includes the functions of selective attention (the capacity to select and orientate its attention on relevant information and to maintain it) and divided attention (the capacity to allocate attention on several sources of information). All the processes would be under the control of a more globalizing entity, namely the supervision attentional system, particularly involved during goal-directed behaviors (i.e. executive functioning).

Attention functions are crucial because they are the prerequisite to the functioning of all other cognitive functions.

Executive functions are defined as the set of processes which allows cognitive and behavior control. They are particularly involved when the subject has to adapt himself to a new or complex situation (carrying out no procedural tasks; problem solving). Even though the term “executive functions” usually refers to a unitary concept, it includes a large number of sub-processes. Among these, the most prominent processes are action initiation, planning, organization, cognitive flexibility, cognitive control, emotion control or conflict monitoring. It is believed that their coordination makes possible the success of self-generated action or behavior [13], and efficiency in dealing with the environment intentionally. In the case of severe executive functioning disturbances [14], patients behave as if they were completely subject to environment (e.g. imitation behavior, lack of control and desinhibition, stereotypic actions, or perseverations).

Social cognition encompasses all psychological processes involved in the comprehension and the regulation of social behaviors. It includes a number of skills in which Theory of Mind (ToM) and empathy are the most representative. The former is referred to a unique form of metacognitive ability, which makes it possible to attribute mental states to oneself or others, like intentions, emotions, motives or beliefs [15]. ToM allows establishing causal links between behaviors and the hypothetical psychological reasons which have induced them [16]. For this reason, such a brain function is thought as one of the pedestal on which social cognition is supported, authorizing successful social relations and behaviors. As for empathy, it can be defined briefly as the ability to recognize and share an emotional experience [17–19].

These two social cognitive functions are very important for the appropriateness of behavior. For example, ToM disturbances are the cognitive landmark of a variety of neuropsychiatric or neurodevelopmental condition like schizophrenia or autism spectrum disorders [20]. A severe lack of empathy characterizes psychopathy or antisocial personality disorders [21].

As mentioned above, surgery, chemotherapy, and/or radiotherapy constitute the main therapeutic options that may be proposed to DLGG patients, often completed by antiepileptic drugs. The effects of these different treatments on cognitive functions have been reported in several studies.

Concerning surgery, provided that tumor removal is performed in awaken conditions, allowing intraoperative brain mapping and maximal resection according to functional boundaries (see Chapters on Surgery for DLGG by Duffau), a transient worsening in cognitive processing is often observed. Most of these cognitive deficits (see below) resolved within 3 months [22], thanks to brain plasticity [23] which is presumably potentiated by the surgical act itself and by individualized cognitive rehabilitation.

Regarding radiotherapy, several studies showed that DLGG patients who received local radiotherapy experienced late-delayed (mean of 12 years after diagnosis) treatment-related disorders in cognitive functioning, especially in attentional functioning. Of note, these disorders were regularly associated with radiological abnormalities, compared with patients who were radiotherapy naïve [24, 25]. Moreover, a phase III trial showed that early radiotherapy has no impact on overall survival in DLGG patients [26]. Therefore, authors suggest that deferring radiotherapy treatment might be the most beneficial strategy to cognitive status.

Concerning chemotherapy, some authors have recently suggested that it might be a valuable therapeutic alternative in the management of patients with DLGG considered as inoperable (or not re-operable) because of an extensive involvement of eloquent areas, or because of invasion of contra-lateral hemisphere [27]. Interestingly, patients who benefited from this therapeutic strategy, namely neo-adjuvant chemotherapy followed by surgical resection after tumor shrinkage, presented with only slight cognitive disturbances, mostly related to glioma location [28].

In any case, without treatment, malignant degeneration is invariably observed in DLGG. According to the guidelines of the European Association of NeuroOncology, surgical resection is now considered as the first therapeutic option for DLGG patients [29]. The extent of resection has been demonstrated to have a significant impact on the natural history of the disease, by delaying malignant transformation and increasing overall survival [30, 31]. Given that this lesion is preferentially located in brain areas involved in sensory-motor and language functions [32], this surgical management has to be led in awaken conditions, in order to check online patients’ cognitive functioning (for which a significant inter-individual variability has extensively been reported) [33, 34]. This therapeutic (and not “wait and see”) attitude allows achieving a challenge with two antagonist goals: to maximize the extent of resection while preserving functional areas, in order to increase patients’ survival without inducing a worsening of their QoL—or even by improving it [35].

Therefore, the surgical management of DLGG patients has to be highly controlled and to follow a sequential succession of therapeutic stages well defined, that begins at the moment of the diagnosis and never ends (see Fig. 18.2). This dynamic strategy encompasses the involvement of a pluri-disciplinary team, which in the peri-operative period, is constituted by the neurosurgeon, anesthesiologist, speech-therapist and/or neuropsychologist, and nurses.

The speech-therapist and/or neuropsychologist have an important role to play in this management. They have to assess cognitive functioning of patients at different peri-operative times, in order to highlight their cognitive status and the efficiency of their own brain plasticity. To achieve this assessment, not only several objective tests but also subjective questionnaires and complaints inventory may be used. Moreover, the speech-therapist and/or neuropsychologist, who will be near the patient during surgery, have to explain clearly the modalities of the surgical procedure as well as the active role the patient, crucial to allow the neurosurgeon to achieve a successful resection. Indeed, the patient should be concentrated and motivated during all the awake period, to enable the neurosurgeon to establish relevant anatomo-functional correlations. This latter aspect of the management is as important as the assessment of cognitive functioning.

It is obvious that the choice of cognitive tests depends on the goal of the assessment, that is, patient care (including peri-operative evaluations) versus patient longitudinal follow-up. Cognitive functioning assessment in the context of patient care must take into account several constraints: temporal constraints, on the one hand, especially concerning intra-operative assessments, and physical and psychological associated signs, on the other hand, due to the tumor itself, but also to reactive psychological distress and treatments—especially antiepileptic drugs (AED). Fatigue is the most reported physical associated sign, and it is correlated with reduced concentration, motivation and activity. There seems to be no relation between fatigue and tumor laterality, or between fatigue and type of neurosurgical intervention (biopsy versus resection). On the other hand, fatigue is associated with AED use [36]. Psychological distress and mood disturbances associated with the disease may also lead to attention disorders and decreased motivation, and thus affect cognitive functioning [37]. In the context of patient care, we should get the most sensitive information as possible about cognitive functioning, independently of disorders induced by physical and psychological associated signs. For instance, in the context of pre-operative examination, we have to assess present (i.e. the day just before the surgery) patient cognitive functioning in order to understand his own brain functional organization and the efficiency of brain plasticity, to give in a way certain clues concerning the possible extent of resection. This pre-operative assessment must be performed in a given time, keeping in mind the understandable psychological consequences induced by the prospect of the imminent brain surgery. Now, extensive cognitive assessments are time-consuming and may fatigue the patient entailing biased results. Thus, cognitive assessments in the context of patient care should be in the same time individualized, sensitive, relevant, but not too long (ideally, each assessment should not exceed 1 h).

Cognitive functioning assessment in the context of longitudinal follow-up should be more extensive, because we are facing neither temporal constraints nor acute psychological distress. In this setting, the use of comprehensive series of tests, possibly administered during several sessions to avoid fatigue, is relevant and of great interest for many reasons: to understand accurately patients cognitive functioning, to put the bases of a possible cognitive rehabilitation, and to control its effects periodically. Of course, the tests used in this context have to be sensitive, valid and reliable. Moreover, longitudinal cognitive assessments should be administered with a sufficient delay between each other (at least 6 months), in order to avoid practice effects.

The surgical management of a DLGG patient is highly controlled and it always follows the same temporal organization (see Fig. 18.2). Cognitive evaluations are administered 4 times peri-operatively: the day before surgery, during surgery, 3–5 days after surgery and 3 months after surgery. Then, cognitive functioning is assessed periodically.