A mosquito bites and a butterfly flies: A specific response type of frontal patients in a similarity task

Neuropsychologia. 2018 Aug;117:371-378. doi: 10.1016/j.neuropsychologia.2018.06.022. Epub 2018 Jun 26.


Background: Patients with neurodegenerative diseases affecting the frontal lobes have difficulties in categorization tasks, such as the similarity tasks. They give two types of unusual response to the question: "In what way are an orange and a banana alike?", either a differentiation ("one is yellow, the other is orange") or a concrete similarity ("they are sweet").

Objective: To characterize the categorization deficit of frontal patients and develop a short diagnostic tool to assess the nature of these difficulties.

Method: We analyzed the responses provided by frontal and non-frontal neurodegenerative patients in a novel verbal similarity task (SimiCat). We included 40 frontal patients with behavioral variant fronto-temporal dementia (bvFTD) and progressive supranuclear palsy (PSP), 23 patients with Alzheimer's disease (AD) and 41 healthy matched controls. Responses that did not correspond to the expected taxonomic category (e.g.: fruits) were considered as errors.

Results: All patients groups were impaired at the SimiCat test compared to controls. Differentiation errors were specific to frontal patients. Receiver operating characteristic analyses showed that a cut-off of two differentiation errors or more achieved 85% sensitivity of 100% specificity to discriminate bvFTD from AD. A short version of the test (<5 min) showed similar discriminative validity as the full version.

Conclusion: Differentiation responses were specific to frontal patients. The SimiCat demonstrates good discriminative validity to differentiate between bvFTD and AD. The short version of the test is a promising diagnostic tool that will need validation in future studies.

Keywords: Alzheimer's disease; Behavioral variant fronto-temporal dementia; Categorization; Neuropsychology; Similarities.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aged
  • Alzheimer Disease
  • Animals
  • Butterflies
  • Case-Control Studies
  • Cognition Disorders / etiology*
  • Concept Formation / physiology*
  • Discrimination, Psychological / physiology*
  • Female
  • Frontal Lobe / physiopathology*
  • Frontotemporal Dementia
  • Humans
  • Insect Bites and Stings
  • Male
  • Mental Status and Dementia Tests
  • Middle Aged
  • Neurodegenerative Diseases / complications*
  • Neurodegenerative Diseases / pathology*
  • Neuropsychological Tests
  • Pattern Recognition, Visual / physiology
  • Supranuclear Palsy, Progressive