Fig. 19.5 a-d. An example of a receptive language paradigm (listening to a reading). Note that the activated areas are closely adjacent to the lesion (glioma) and intermingled with it. The patient underwent surgery and had postsurgical deficits (aphasia)
reading comprehension task consists of reading stories, in which each paragraph is presented at a fixed interval of time, according to the reader's speed. The most common auditory comprehension task consists of listening to stories. The latter is a passive task, which, like sensory paradigms, can also be performed on uncooperative patients.
When visual input is used, one has to consider brain activation induced by visual input, in addition. This activation does not concern the primary visual cortex only, but also the ventral extrastriate inferior temporal/ occipital regions, involved in transferring the modulated inputs to the Wernicke's area. Otherwise, when auditory input is used, this will produce an auditory response in the adjacent auditory cortices of the superior temporal gyri. To isolate Wernicke's area and delete visual/auditory responses, other visual/auditory stimuli (e.g. uppercase/lowercase letters or backward text, respectively) may be used in the contrasting control task. However, this is not the case for presurgical purposes, because auditory/visual areas also have to be spared from the surgery.
Figure 19.5 shows an example of receptive language paradigm (listening to a reading).
Expressive Language Paradigms. This kind of task explores the production aspect of language and elicits eloquent areas corresponding to Broca's area proper (the pars opercularis, BA44, and the posterior portion
of the pars triangularis, posterior BA45, of the inferior frontal gyrus), plus the precentral gyrus of the insula, in the dominant hemisphere.
Most of the numerous existing paradigms can be classified into two main categories: verbal fluency and semantic decision. The main difference between the two is that semantic decision tasks do not explore language production only, but also some working memory functions; the result is the activation of other areas in addition to expressive language ones (see below).
Verbal fluency tasks rely on the ability to produce words in different ways. Worth noting is that the patient is requested to generate words covertly (inner speech), to avoid possible artefacts caused by movements of the lips, tongue and head in active word generation. When the task is of the phonological kind, the patient is visu
ally or verbally cued with a letter of the alphabet at the beginning of each task period and asked to think of as many words as possible that begin with that letter. Of course, the letters change in each task period. When the task is of the semantic kind, the patient is visually or verbally cued with a certain category (e.g. animals, flowers) at the beginning of each task period and asked to think of as many words as possible that belong to that category. During the rest condition, the patient may repeat a single word (e.g. „bla", „bla", „bla"...) or may think of nothing. Receptive language areas are activated by both paradigms, but the phonological task gives a more clear-cut activation than the semantic one .
A verbal fluency task which is very well used and reliable in disclosing lateralization is verb generation from words. A sequence of words is aurally or visually presented to the patient, who has to think of a verb corresponding to each word (e.g. piano ^ to play), whereas the rest condition consists of silence. In addition to Broca's area, other eloquent areas may be activated in the dominant hemisphere: the pars orbitalis of the inferior frontal gyrus, BA47, the middle frontal gyrus, BA46 and 9, and the prefrontal and posterior temporal cortices.
Semantic Decision Tasks. In this kind of task, a couple of words are sequentially presented to the patient, who has to decide if the couple appertain to a certain semantic category stated previously (e.g. synonyms vs.
antonyms, abstract vs. concrete, living vs. non-living, etc.). Rest conditions differ according to whether the task is given aurally or visually. In the first case, couples of tones are presented and the patient has to decide if they are identical or not. In the second case, couples of letter are shown and the patient has to decide if they are written in uppercase or in lowercase. As already mentioned, these tasks activate other areas, besides Broca's area, and these are: the middle and the inferior temporal gyri, fusiform and parahippocampal gyri, the cin-gulate cortex (BA32) and the superior frontal region (BA8) in the dominant hemisphere.
Figure 19.6 shows an example of an expressive language paradigm (words ^ verbs).
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