Lesions studies give a better insight into the causally necessary function of brain struc-tures, whereas electrophysiological methods and fMRI simply demonstrate correlations withpsychological processes.

Lesions present dissociations in cognition which could otherwiseonly have been speculated, and therefore can shape our understanding of the architecture ofthe mind. Psycholinguistic lesion studies usually involve patients who have suffered a sud-den injury (stroke, traumatic head injury) or who suffer from a progressive disorder (PPA,Alzheimer’s) resulting in deficits in cognitive tasks (e.g. speech related tasks). The patient’sperformance in e.g.

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a linguistic task is compared to results of healthy controls which matchthe participant sample in age and education.Lesions studies are flexible regarding participant pool size; they can be done with eithera single patient, to relate an impaired brain area (one with a lesion) to a specific deficitor behaviour, or with a small, homogenous, comparable patient group to see if there is anoverlapping between the patients lesions and a common disorder (the question typicallyasked in this case being “if a group of patients demonstrates a particular linguistic deficit,has there been impairment to a specific area of their brain?”) or, with larger, heterogenousgroups of patients, a voxel based lesion symptom mapping can be done, which determines abrain-behaviour relationship on a voxel basis. A voxel is a (fairly small) 3D unit of volumeused in neuroimaging processes that analyze the role of grey and white matter in e.g. psy-cholinguistic processes.Collection of data in lesion studies consists of both acquisition of psycholinguistic data andneuroimaging data; ideally coincident in time. Psycholinguistic data is gained through lin-guistic tests at different stages of recovery (acute stage, post-acute stage, chronic stage).

Neuroimaging data is acquired with CTs or MRIs, in orde to review or reconstruct the pa-tient’s lesion. This helps locating the lesion and allows for comparison to lesions of otherpatients.Voxel based lesion symptom mapping (VLSM) tools provide statistical analysis ofthe relationship between discrete brain regions and language behaviours on a voxel-to-voxelbasis. A statistical test like a t-test or a general linear model is run at every voxel to comparethe performance in patients whose lesions involve a particular voxel with the performanceof patients whose lesions spare that particular voxel.This procedure involves 4 steps: 1) the patient’s lesions are reconstructed onto a standardizedtemplate an read into analysis; then 2) at every voxel, a statistical test is run to comparethe behavioural language scores of patients with or without a lesion in a particular voxel.3) The resulting test statistics at every voxel are then colour-coded and visualized, to allowfor better analysis and comparison after 4) statistical corrections are applied in order todisplay only voxels which meet pre-specified significance levels. The analysis is facilitatedby specialized imaging software (which is often free, like the MRICron). To help locate thevoxels, a brain atlas template like AAL can be yoked to the VLSM results.

This allowsfor direct comparison with PET or fMRI scans of age- and education matched healthyindividuals. VLSM furthermore offers the ability to include a wide range of patients whodon’t necessarily share a lesion in a particular area or who show the same deficit. On theother hand, this leads to a bigger participant pool being required, as otherwise, the statisticalpower wouldn’t be big enough.For progressive disorders where no lesion is present, an alternative method called VBM(= voxel based morphometry), which measures cortical thinning by comparison of voxelbased intensity changes of tissue, which is then correlated with behavioural performancebetween groups of patients, is used.Another relatively new technique, next to other non-invasive brain stimulation tech-niques like tDCS, is TMS. Transcranial magnetic stimulation (TMS) can be performed onhealthy individuals to stimulate a temporary cognitive dysfunction resembling a lesion.

Thepurpose for the method lies in the functional reorganization of artificial brain lesions, as itcannot take place in the short amount of time during which the stimulation occurs. Otherpotential benefits have been reported, like improvement of functioning during/after TMSconditions, but these effects need further research to be confirmed.To conclude, careful characterization of the deficits following lesions and their changeover time provides valuable information not only about the constellation of impairmentsproduced, but also about their compensation and possible resolution over time. Data fromlesion patients seem to show how dynamic brain networks depend on the function of par-ticular components and how cognition can be at least partially decomposed into modulesof sorts. In short, lesion studies offer unique value for psycholinguistic research and otherresearch concerning the human brain since they, in contrast to other neuroimaging tech-niques, provide the ability to evaluate which brain areas are most critical/important fo