Chiara Finocchiaro

All Talk and No Action: A Transcranial Magnetic Stimulation Study of Motor Cortex Activation during Action Word Production

A number of researchers have proposed that the premotor and motor areas are critical for the representation of words that refer to actions, but not objects. Recent evidence against this hypothesis indicates that the left premotor cortex is more sensitive to grammatical differences than to conceptual differences between words. However, it may still be the case that other anterior motor regions are engaged in processing a words sensorimotor features. In the present study, we used singleand paired-pulse transcranial magnetic stimulation to test the hypothesis that left primary motor cortex is activated during the retrieval of words (nouns and verbs) associated with specific actions. We found that activation in the motor cortex increased for action words compared with non-action words, but was not sensitive to the grammatical category of the word being produced. These results complement previous findings and support the notion that producing a word activates some brain regions relevant to the sensorimotor properties associated with that word regardless of its grammatical category.

A Case Study of Primary Progressive Aphasia: Improvement on Verbs After rTMS Treatment

This case-report shows that high frequency repetitive Transcranial Magnetic Stimulation (hf-rTMS), applied to the left prefrontal cortex, may improve the linguistic skills in Primary Progressive Aphasia (PPA). The patients performance was evaluated on a battery of language production and memory span tasks, before and after two hf-rTMS treatments and one SHAM treatment. We observed a significant and lasting improvement of the patients performance on verb production following the application of hf-rTMS versus Baseline and SHAM conditions. This finding suggests that hf-rTMS may directly strengthen the neural connections within an area of metabolic dysfunction and encourages the use of rTMS as an alternative therapeutic tool for neurodegenerative forms of aphasia.

Contribution of motor representations to action verb processing

Electrophysiological and brain imaging studies show a somatotopic activation of the premotor cortex while subjects process action verbs. This somatotopic motor activation has been taken as an indication that the meaning of action verbs is embedded in motor representations. However, discrepancies in the literature led to the alternative hypothesis that motor representations are activated during the course of a mental imagery process emerging only after the meaning of the action has been accessed. In order to address this issue, we asked participants to decide whether a visually presented verb was concrete or abstract by pressing a button or a pedal (primary task) and then to provide a distinct vocal response to low and high sounds played soon after the verb display (secondary task). Manipulations of the visual display (lower vs. uppercase), verb imageability (concrete vs. abstract), verb meaning (hand vs. foot-related), and response effector (hand vs. foot) allowed us to trace the perceptual, semantic and response stages of verb processing. We capitalized on the psychological refractory period (PRP), which implies that the initiation of the secondary task should be delayed only by those factors that slow down the central decision process in the primary task. In line with this prediction, our results showed that the time cost resulting from the processing of abstract verbs, when compared to concrete verbs, was still observed in the subsequent response to the sounds, whereas the overall advantage of hand over foot responses did not influence sound judgments. Crucially, we also observed a verb-effector compatibility effect (i.e., foot-related verbs are responded faster with the foot and hand-related verbs with the hand) that contaminated the performance of the secondary task, providing clear evidence that motor interference from verb meaning occurred during the central decision stage. These results cannot be explained by a mental imagery process that would deploy only during the execution of the response to verb judgments. They rather indicate that the motor activation induced by action verbs accompanies the lexico-semantic processes leading to response selection.

Morphological complexity reveals verb-specific prefrontal engagement

Neuropsychological evidence and recent rTMS studies strongly suggest that damage or inhibition of left prefrontal areas may result in specific impairment of verb morphosyntactic processing. However, functional imaging studies have so far failed to identify an area specifically related to grammatical aspects of verb knowledge. To date very few functional studies have been conducted in languages other than English, a language with limited inflectional morphology. In the present study, we make the hypothesis that neuronal responses for verb grammatical processing may be more or less evident depending on the morphological complexity of verbs in a given language. Exploiting the morphologically rich verbal paradigm typical of the Italian language we implemented an event-related functional MRI design to identify cortical regions that were active when subjects produced nouns or verbs in the context of short phrases. Results showed an area of verb-specific activation for real verbs in a small left frontal region corresponding to the intersection of BA10, BA46 and BA 47. We interpret the results as revealing that languagespecific morphological properties may modulate the pattern of grammatical specific activations. Specifically, higher degrees of morphophonological complexity may engage a greater variety of morphophonological operations, thus enhancing the possibility of activations specific for a given grammatical class.

The Production of Pronominal Clitics: Implications for Theories of Lexical Access.

In three experiments we investigated the locus of the frequency effect in lexical access and the mechanism of gender feature selection. In Experiment 1, participants were asked to produce gender-marked verb plus pronominal clitic utterances in Italian (e.g., “portalo” (bring it [masculine]) in response to a written verb and pictured object. We found that pronominal clitic production is sensitive to the frequency of the noun it replaces. This result locates the effect of word frequency in lexical access at the level where a words grammatical features are represented. In Experiments 2, 3A, and 3B we used a picture-word interference naming task and found that the gender of a distractor word does not affect the production of gender-marked clitics. This result, together with those of Experiments 3A and 3B, which show a semantic interference effect and the absence of a phonological facilitation effect in clitic production, respectively, allows the inference that the retrieval of grammatical gender is an automatic consequence of lexical node selection and not an independent selection process that operates on the principle of selection-by-activation level.

About the locus of the distractor frequency effect: Evidence from the production of clitic pronouns

In this study, we report results from two experiments in which pictures were shown with superimposed distractors that varied along two dimensions: frequency (high vs. low) and semantic relation with respect to the picture (related vs. unrelated). In one condition of Experiment 1, participants named pictures with a noun utterance; in the other condition of Experiment 1 and in Experiment 2 participants named pictures with a pronominal utterance. Low frequency distractor words produced greater interference with respect to high frequency words in noun production, but not in pronoun production. Critically, a semantic interference effect, greater interference in the semantically related than unrelated condition, was reported in both experiments, suggesting that distractor words were equally processed in both noun and pronoun conditions. These results are discussed in the context of current models of picture–word interference.

Verb Actionality in Aphasia: data from two aphasic subjects

Many reports of brain-damaged subjects have dealt with the semantics of nouns. By comparison, verb semantics has received little attention in the neuropsychological literature. In this paper we analyze the effects of the actional category of verbs on the performance of two Italian-speaking aphasic subjects in auditory comprehension and oral production tasks. Both subjects are sensitive to the actional value of verbs. In subject GSC, State verbs were significantly more preserved than other verb categories; subject AMA fared better when naming Process verbs than other verb types. These differential patterns of impairment cannot be reduced to effects of abstractness/concreteness or of frequency, and appear to be due to genuine Actionality effects. Results from the present study support the view that actional category information is a fundamental organizational principle of semantic knowledge of verbs in the brain.

Sensitivity to the verb [±agentive] feature: the case of an aphasic subject

Abstract Available data show that semantic categories of nouns can be selectively impaired in aphasia. This study investigates whether category-specific effects can also be obtained with verbs. The [±agentive] feature is addressed, drawing on the case of an aphasic subject (CAN). CAN showed a clear dissociation between [+agentive] verbs vs. [−agentive] verbs (significantly more impaired). This pattern of performance was consistent across a battery of verb production tests (both in isolation and in context) and grammaticality judgements. The results provide evidence for the importance of the agentivity feature in the representation of verbs.

The dissociability of lexical retrieval and morphosyntactic processes for nouns and verbs: A functional and anatomoclinical study

Nouns and verbs can dissociate following brain damage, at both lexical retrieval and morphosyntactic processing levels. In order to document the range and the neural underpinnings of behavioral dissociations, twelve aphasics with disproportionate difficulty naming objects or actions were asked to apply phonologically identical morphosyntactic transformations to nouns and verbs. Two subjects with poor object naming and 2/10 with poor action naming made no morphosyntactic errors at all. Six of 10 subjects with poor action naming showed disproportionate or no morphosyntactic difficulties for verbs. Morphological errors on nouns and verbs correlated at the group level, but in individual cases a selective impairment of verb morphology was observed. Poor object and action naming with spared morphosyntax were associated with non-overlapping lesions (inferior occipitotemporal and fronto-temporal, respectively). Poor verb morphosyntax was observed with frontal-temporal lesions affecting white matter tracts deep to the insula, possibly disrupting the interaction of nodes in a fronto-temporal network.

Thematic role assignment in the posterior parietal cortex: A TMS study.

Verbs denote relations between entities acting a role in an event. Thematic roles are essential to the correct use of verbs and involve both semantic and syntactic aspects. We used repetitive Transcranial Magnetic Stimulation (rTMS) to study the involvement of three different left parietal sites in the understanding of thematic roles. In a sentence-to-picture matching task, twelve participants were asked to judge whether or not a given picture matched with a written sentence. Pictures represented simple reversible actions, and sentences were in the active or passive diathesis. Whereas both active and passive sentences require the correct encoding of thematic roles, passives also imply thematic reanalysis, as the canonical order of thematic roles is systematically reversed. The experiment was divided in three sessions. In each session a different parietal site (anterior, middle, posterior) was stimulated at 5 Hz in an event-related fashion, time-locked to the presentation of visual stimuli. Results showed increased accuracy for passive sentences following posterior parietal stimulation. The effect appeared to be (a) TMS-related, as no effect was observed in a control, no-TMS experiment with eighteen new participants; (b) independent from semantic processes involved in word-picture association, as no TMS-related effects were observed in a picture-word matching task. We interpret the results as showing that the posterior parietal site is specifically involved in the assignment of thematic roles, in particular when the correct interpretation of a sentence requires reanalysis of temporarily encoded thematic roles, as in passive reversible sentences.