New and exciting result on language in Huntington disease!

On February 3, 2017 by Joana Rossello

Together with Wolfram and Cati, and other colleagues from different institutions led by Ruth de Diego, some days ago we submitted the first systematic analysis of spontaneous speech as performed in a story-telling task (Cinderellla) and compared with matched controls. Central to our contribution was the design of a classificatory procedure to fine-grain the linguistic profile of HD including pre-symptomatic gene-carriers and symptomatic patients.

The results appear to us to be important in at least three interrelated regards. Firstly because they show that the subcortical striatal contribution to language deserves to be investigated thoroughly. It is worth to know that HD, in contrast to other polygenic and consequently brain diversified pathological or atypical cognitive profiles, is determined by an autosomal dominant mutation which leads to a well-known process of neural degeneration that affects mainly the striatum, a subcortical gray matter structure near the center of the brain.

Secondly, our results suggest that a grammatical assessment is more sensitive than the one based on the acoustics of speech to keep track of the course of the disease, including its initial stage. And, thirdly, this paper might pave the way for a better understanding of the well-known but nevertheless striking fact that a mainly motor disease shows up in cognitive deficits even before motor signs are reported.

In connection with the latter, our analysis has been able to show that the speech of pre-symptomatic gene carriers in contrast to controls’ presents with a linguistic impairment undetectable by means of other behavioral, neuropsychological or neural measurements and preceding observable motor and generic cognitive function deterioration. Moreover, the initial linguistic impairment affects high order functions such as Reference and Connectivity, which were the two domain variables that significantly distinguished pre-symptomatic gene carriers from controls. The former, Reference, captured problems in the referential use of language that in story-telling translated in difficulties to identify story characters and objects and to establish topics of the discourse. The latter captured how clauses are grammatically combined to yield propositional and discourse reference. Also Fluency (truncations, repetitions, pauses, etc.) and Concordance (grammatical agreement) were affected although not significantly at the prodromal stage.

To us, these overall results might only be added as further evidence of the prior cognitive impairment in HD if language was taken to contribute rather than result from cognition. An alternative modular view with language abstracted from communication and thought, which will be also logically possible, is inherently less parsimonious and difficult to conciliate with the existence of subsequent motor problems also in the domain of speech.

It is telling in this regard that the high order linguistic (mal)function in Reference and Connectivity is associated more clearly with low order linguistic (mal)function (Fluency and Agreement) than with other neuropsychological or neural measurements. At this point our suggestion here ‑‑not in the paper, which is more constrained– is that the hierarchically organized linguistic faculty integrates different basic functions (motor, sensory, executive, attentional, mnemonic) across all the hierarchical levels, from sound articulation and perception to linguistic, rational complex thought. This integration requires that the functional components entering the composite domain work optimally at the individual level when a high demanding cooperative, joint work is at stake, namely speech and language. Let’s consider this optimal functioning an ‘integration threshold’. An integration threshold would be by definition higher than the amount of function necessary for simpler tasks. To illustrate, think of running in comparison to walking: the former would require an integration threshold than the latter would not. According to this view, current neuropsychological battery tests might not be sensitive to the integration threshold each component or basic function is required to reach in co-working. This conjecture seems to deserve some careful thought if only because it opens an explanatory avenue for the above mentioned striking fact, namely that a mainly motor disease such as HD starts with a cognitive impairment.

A systematic linguistic profile of spontaneous narrative speech in pre-symptomatic
and early stage Huntington’s disease
Wolfram Hinzen, Joana Rosselló, Cati Morey, Estela Camara, Clara Garcia-
Gorro, Raymond Salvador, Ruth de Diego-Balaguer

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