Science of Aphasia 5 Cross Linguistic Aspects of Aphasia ...

Neuroanatomical correlates of selective impairments of nouns and verbs
Silvia Aggujaro 1 , Davide Crepaldi 1 , Caterina Pistarini 2 , Mariangela Taricco 3
and Claudio Luzzatti 1
1 Department of Psychology, University of Milano-Bicocca
2 S. Maugeri Foundation, Montescano Medical Center, Pavia
3 Rehabilitation Unit, G. Salvini General Hospital, Passirana, Milano
INTRODUCTION
Theoretical linguistics suggests that the representation of verbs (V) and nouns (N) is independent, reflecting the
functional difference of these word classes in syntax. Observation of brain damaged patients demonstrates the
existence of double dissociations with disproportionate impairments of either Vs or Ns (e.g. Berndt et al. 1997).
However, the mechanisms underlying N-V dissociations are not yet well defined; some authors have considered
them to be proof that the mental organization of Ns and Vs is separate, while others (Bird, Howard and Franklin,
2000), maintain that Ns and Vs do not dissociate on the basis of a true grammatical class effect, but on that of an
artifact due to the different kind of underlying semantic knowledge.
The primary aim of the present study was the identification of the anatomical loci of the lesions causing
selective impairments of Vs and Ns. In addition, an attempt was made to disentangle the effect of imageability
from a possible effect of the degree of motor functional mental images underlying verbs (actionality), and,
finally, to analyze the relation of these variables and the site of the underlying cerebral lesion.
MATERIALS AND METHODS
Subjects
Fifteen aphasic patients suffering from disproportionate impairment of verbs (DIV) and five patients suffering
from disproportionate impairment of nouns (DIN) participated in the study.
N-V dissociations were identified by evaluating naming abilities of Ns and Vs through a picture-naming task.
Disproportionate impairment on either Vs or Ns was identified by a logistic regression analysis. The majority of
the DIN cases also showed a word frequency effect; all 15 DIV cases showed an imageability effect.
Task
The picture naming task used to test the naming ability of the participants is composed of 30 pictures of objects
(15 natural objects and 15 artifacts) and 40 pictures of actions (of which 12 verbs with low degree of actionality,
14 with an intermediate and 14 with a high degree of actionality).
The major lexical-semantic variables (oral word frequency, age of acquisition, familiarity with the underlying
concepts and imageability) were included in the experimental design.
Imageability and actionality ratings
Each of the items included in the naming task was scored by a group of 20 adult controls for visual imageability
using a 1-to-7 rating scale (Luzzatti et al. 2002).
The degree of fine motor planning of hand movements (actionality) underlying the action denoted by each of the
verbs elicited by the naming task was tested by a group of 25 healthy undergraduate students that estimated the
degree of actionality using a 1-to-7 scale.
Mapping of brain lesions from NMR & CT scan pictures
Lesions were reconstructed and mapped onto a lateral template of the brain.
RESULTS
Localization of the brain lesions causing DIN and DIV
In a first part of the study the areas of the brain involved in the storage of lexical representations of Vs and Ns
were investigated by localizing the brain lesions causing disproportionate impairment to the retrieval of these
lexical categories.
In the majority of the DIN patients, the lesion involved the medial part of the middle and inferior left temporal
gyri (Broadmann area (BA) 21, 20, 37). On the contrary, the lesions found in DIV patients clustered in two major
subsets: in the first group of patients, the focal brain damage involved the posterior part of left temporal lobe and
the inferior parietal gyrus (BA 21 posterior, 37 superior, 39, 40); in the second group, the lesion involved the left
frontal, temporal and parietal perisylvian territory (BA 44, 40, 22, 41, 42), causing complete destruction of the