FRONTAL ASLANT TRACT AND ITS ROLE IN NORMAL SPEECH AND PRIMARY PROGRESSIVE APHASIA

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Background. Primary progressive aphasia (PPA) is a clinical dementia syndrome characterized by the progressive impairment of language functioning affecting other cognitive domains as well. Nowadays it is known that PPA is associated with the impairment of frontal aslant tract (FAT) - direct pathway connecting Broca’s region (inferior frontal gyrus - pars opercularis) with the anterior cingulated and pre-supplementary motor area. Aim. To study the normal FAT function and the relation between PPA and FAT impairment based on the reviewed articles. Material and Methods. The articles from PubMed databases published in the last 5 years were analyzed. Key words used: «frontal aslant tract», «primary progressive aphasia», «aphasia», «white matter». Results and Discussion. During the analysis it was found that patients with PPA possess many macro-and microstructural FAT abnormalities, such as cortical atrophy in the posterior frontal regions, changes in number of streamlines, fractional anisotropy and radial diffusivity, which underlie verbal fluency deficits in patients with PPA. Furthermore, intraoperative stimulation of FAT causes stuttering, and stimulation of the pre-supplementary motor area and anterior cingulated cortex connected by FAT produces vocalization and arrest of speech. In addition, lesions in these areas result in speech impairment from mutism to mild altered fluency. Conclusions. The frontal aslant tract is a white matter fascicle that provides verbal fluency. When impaired, it fails to function properly causing speech dysfluencies. Moreover, since it connects inferior frontal gyrus (pars opercularis) with the anterior cingulated and pre-supplementary motor area, it can indirectly control the speech initiation.