**3.2 Task selection and adaptation**

The selection of tasks for intraoperative monitoring is done during the presurgical phase considering the location of the lesion, the age, and the educationalcultural level of the patient and cognitive abilities. To minimize the risk of false positives, only those items in which the patient performs flawlessly will be selected.

Using language domain as an example of function monitored during an awake surgery, the most common tasks used are naming objects, counting, naming verbs, naming famous people, reading sequences, naming colors, naming days of the week or months of the year, or repetition. These tasks can be associated with other motor control tasks such as the movement of an arm or tapping tasks or previous tasks such as promoting spontaneous language through a conversation about the patient's life (with information that has been obtained in the presurgical evaluation), or if the patient is comfortable or feels pain or cold, etc.

Regarding language monitoring, one must bear in mind:

**Language without semantic content:** Automatic speech tasks require motor planning and articulatory processing. To evaluate this type of language, the patient is encouraged to recall the numbers from 1 to 20 or to say the months of the year. This type of tasks uses overlearned sequences of words. Repetition of phonemes quickly (e.g., Fa-Ma-Ba) or word/nonword repetition can also be used.

**Lexico-semantic processes:** The most frequently used task is the presentation of drawings or pictures of objects for naming. In several studies, an introductory phrase has been added (this is a ...). Following Ojemann and Mateer, adding the introductory phrase allows us to distinguish between an anomic error and a speech arrest, but a failure could be the result of an orthographic mistake or an inability to read. Another frequently used task is action-naming [15]. A drawing, image, or video of a person performing an action are presented to the patient and the patient must name the action in the infinitive. The famous face naming requires the same processes as object naming, adding facial recognition and access to biographical information. Auditory object naming is used too. In this case, the patient hears a description of the object and its use, and then it must be named.

The pyramids and palms test is frequently used in intrasurgical monitoring. The patient must choose between two stimuli that are associated with an image presented at the top of the screen. This test allows to know the capacity of access to the semantic information of the pictures and the words and associate this information.

**Grammatical processes:** Naming actions (already described previously) have been used frequently. Other tasks are reading sentences slowly or complete sentences, in which one word is missing (to allows assess different grammatical), sentence repetition, writing sentences.

#### **3.3 Evaluation of presurgical imaging studies**

When the decision to perform an awake surgery must be taken, one can use the information provided by a set of tools that allow us to decide the degree of eloquence for a specific function. The location of the lesion or the clinical information is not enough to evaluate the relationship between the lesion and its functional boundaries.

However, in this point, it is essential to define more precisely what we understand as an "eloquent area." This concept has significantly evolved in the last decades, from considering eloquent areas only those involved in motor control and language, to considering other regions involved in sensorial and cognitive processing. The evolution of this concept is also associated with the better understanding

of brain function that has currently been achieved. The "localizationist" vision has again been abandoned and substituted by an hodotopic view, where connectivity between one brain regions to another becomes relevant to the development of a function [16]. Furthermore, the hodotopic model includes a dynamic representation of functional systems (i.e., that change with time), fitting better with the current knowledge in brain plasticity. Therefore, an "eloquent area" can be considered as the gray matter and white matter pathways that are essential for the development of a specific function that, in the personal context of each patient, must be preserved. Each "eloquent area" can change its location with time, thanks to brain plasticity mechanisms that are activated in disease situations.

The identification of eloquent areas before a surgical procedure for a brain tumor may help in different ways:


One of the tools that have demonstrated to be useful in achieving these aims is magnetic resonance imaging (MRI) [17]. The use of this technique is widely extended, and it constitutes an essential part of the diagnostic protocol of a brain lesion. Apart from the images acquired for diagnosis, additional sequences and procedures can be performed to obtain functional information. More specifically, the use of functional magnetic resonance imaging (fMRI) and diffusion tensor imaging (DTI) allows us to identify cortical regions and white matter tracts, respectively, that are involved in specific functions [18].

Functional MRI is based on the detection of changes in magnetization secondary to the levels of oxyhemoglobin, which increases in brain regions whose neurons increase their activity to be able to perform a specific task. fMRI has been demonstrated to be useful in the identification of the somato-motor regions using simple motor tasks with high sensitivity and specificity. However, the reported values of sensitivity and specificity for the identification of language processing areas are much lower. This difference is more pronounced during the evaluation of the sensitive component of this complex task. Furthermore, there is also a lack of evidence about the use of fMRI to map the regions involved in other cognitive tasks in patients with a brain tumor, although a significant amount of literature has described the relationship between the activities in specific regions with a specific function, but they are all in the research environment. In this regard, the development of new language tasks or paradigms to be used in fMRI studies might improve the reliability of the information provided by this technique. In the same way, cognitive tasks adapted to fMRI should be tested in brain tumor patients, to identify their usefulness in presurgical brain mapping.

Regarding the selection of fMRI tasks for presurgical mapping, one must bear in mind that there is a significant restriction of movement inside the scanner; thus, the selected task must not be associated with the excessive movement. Furthermore, we consider that the fMRI task should be as similar as possible to the task that is going to be performed during the surgical procedure.

The combination of fMRI with DTI would give us much information that may be useful to predict the cortical regions that will be positive during stimulation as well as the white matter tracts that are associated with the tumor. All this information will help us to decide which tasks will be used during the procedure; to decide the location and the size of the craniotomy; to predict the entry point to perform the corticectomy; and to give a precise information to the patient and relatives about the risks and prognosis.

## **3.4 Training and preparation of the patient**

Once an awake craniotomy is considered for a patient, a multidisciplinary team should discuss about the feasibility of performing this procedure in this patient. The multidisciplinary team includes, necessarily, anesthesiologists, neuropsychologists/ speech therapists, and neurosurgeons. Additionally, this team could also include radiologists and clinical psychologists. These professionals would finally decide if the patient is a good candidate for an awake surgery and they will plan the training of the patients for the procedure.

Keeping awake during the whole or part of a surgical procedure that involves the brain is an additional stress not only for the patient but also for the surgical team. This stress would be associated with the beliefs or expectations that may have the patient in terms of pain, immobility, or the experiencing of intraoperative complex situations. Regarding the surgical team, the lack of familiarity with the procedure may hinder the anticipation of possible complications that may appear during the surgery.

Bearing all this in mind, to achieve a successful procedure, it is essential that both the patient and the surgical team have to be instructed and trained before the surgery.

Regarding the surgical team, the ideal would be to designate a specific team for this kind of surgery. A group of anesthesiologists, surgeons, and nurses, after adequate training, should accumulate experience in such procedures, avoiding global changes in the members of the team, but allowing the occasional participation of new members to acquire experience.

On the other hand, regarding the training of the patient, we consider that he/she must know and understand the purpose of each step of the procedure. The patient must understand why an awake surgery is planned and what are its aims. After that, the patient must be explained in detail how the procedure will be taken place, from the arrival to the surgical area, to the admission in the postsurgical area. Apart from all the explanations, it is adequate to perform a specific training that should include the tasks that have been selected for the surgery, the positioning, and the layout of the operating room. In this sense, it is advisable that this training is performed in simulation conditions, mimicking the conditions that the patient will find during the surgery.

In our center, the training of the selected tasks is performed by the same neuropsychologist who has evaluated the patient and who is going to be during the surgery. This reinforces the link between the patient and the professional and contributes in reducing the anxiety and stress related to the procedure. Furthermore, the neuropsychologist can use the training sessions to adapt the tasks to the situation and features of the patient. This may lead to a more efficient procedure, thus lesser surgical times. The simulation of the procedure (positioning and operating room distribution) is performed in a room with a stretcher and with furniture that mimics those, we found in an operating room. The patient is explained about the positioning and is indicated about the interlocutors during the surgery. This may help to know the people with whom the patient must communicate with. The number of training sessions is adjusted by the functional and cognitive status of each patient. We usually recommend at least two training sessions for tasks and two for simulating the procedure.
