title: Graph analysis of verbal fluency test discriminate between patients with Alzheimer's disease, mild cognitive impairment and normal elderly controls.
abstract: Verbal fluency is the ability to produce a satisfying sequence of spoken words during a given time interval. The core of verbal fluency lies in the capacity to manage the executive aspects of language. The standard scores of the semantic verbal fluency test are broadly used in the neuropsychological assessment of the elderly, and different analytical methods are likely to extract even more information from the data generated in this test. Graph theory, a mathematical approach to analyze relations between items, represents a promising tool to understand a variety of neuropsychological states. This study reports a graph analysis of data generated by the semantic verbal fluency test by cognitively healthy elderly (NC), patients with Mild Cognitive Impairment-subtypes amnestic (aMCI) and amnestic multiple domain (a+mdMCI)-and patients with Alzheimer's disease (AD). Sequences of words were represented as a speech graph in which every word corresponded to a node and temporal links between words were represented by directed edges. To characterize the structure of the data we calculated 13 speech graph attributes (SGA). The individuals were compared when divided in three (NC-MCI-AD) and four (NC-aMCI-a+mdMCI-AD) groups. When the three groups were compared, significant differences were found in the standard measure of correct words produced, and three SGA: diameter, average shortest path, and network density. SGA sorted the elderly groups with good specificity and sensitivity. When the four groups were compared, the groups differed significantly in network density, except between the two MCI subtypes and NC and aMCI. The diameter of the network and the average shortest path were significantly different between the NC and AD, and between aMCI and AD. SGA sorted the elderly in their groups with good specificity and sensitivity, performing better than the standard score of the task. These findings provide support for a new methodological frame to assess the strength of semantic memory through the verbal fluency task, with potential to amplify the predictive power of this test. Graph analysis is likely to become clinically relevant in neurology and psychiatry, and may be particularly useful for the differential diagnosis of the elderly.
authors.affiliation: Laboratory of Clinical Neuroscience Investigations, Federal University of Minas Gerais Belo Horizonte, Brazil.
authors.forename: Laiss
authors.initials: L
authors.lastname: Bertola
authors.affiliation: Brain Institute, Federal University of Rio Grande do Norte Natal, Brazil.
authors.forename: Natália B
authors.initials: NB
authors.lastname: Mota
authors.affiliation: Physics Department, Federal University of Pernambuco Recife, Brazil.
authors.forename: Mauro
authors.initials: M
authors.lastname: Copelli
authors.affiliation: Laboratory of Clinical Neuroscience Investigations, Federal University of Minas Gerais Belo Horizonte, Brazil.
authors.forename: Thiago
authors.initials: T
authors.lastname: Rivero
authors.affiliation: Laboratory of Clinical Neuroscience Investigations, Federal University of Minas Gerais Belo Horizonte, Brazil ; Mental Health Department, Faculty of Medicine, Federal University of Minas Gerais Belo Horizonte, Brazil.
authors.forename: Breno Satler
authors.initials: BS
authors.lastname: Diniz
authors.affiliation: Mental Health Department, Faculty of Medicine, Federal University of Minas Gerais Belo Horizonte, Brazil ; Faculty of Medicine, National Institute of Science and Technology - Molecular Medicine, Federal University of Minas Gerais Belo Horizonte, Brazil.
authors.forename: Marco A
authors.initials: MA
authors.lastname: Romano-Silva
authors.affiliation: Brain Institute, Federal University of Rio Grande do Norte Natal, Brazil.
authors.forename: Sidarta
authors.initials: S
authors.lastname: Ribeiro
authors.affiliation: Laboratory of Clinical Neuroscience Investigations, Federal University of Minas Gerais Belo Horizonte, Brazil ; Mental Health Department, Faculty of Medicine, Federal University of Minas Gerais Belo Horizonte, Brazil.
authors.forename: Leandro F
authors.initials: LF
authors.lastname: Malloy-Diniz
keywords: Alzheimer's disease; elderly; graph analysis; mild cognitive impairment; semantic verbal fluency