[Control of inner speech and Gilles de la Tourette's syndrome]

Inner speech is the little voice in the head which comments on everyday life activities. To some aspect, trouble in monitoring the inner speech has been regarded as relevant in auditory hallucinations in psychosis. Another disorder that may involve inner speech is the difficulty inhibiting its vocal utterance (the so-called verbal impulsion ). Verbal impulsion is a classic feature of Gilles de la Tourette's syndrome, during which patients complain of difficulties inhibiting socially undesirable behaviors, especially vocalization (i.e. coprolalia). In a previous paper, we reported on a patient with frontotemporal dementia, whose pathology was revealed by a difficulty inhibiting the verbal utterance of reading (inability to read silently). Later in the course of the disorder, the patient exhibited a severe frontal lobe syndrome with compulsive activities and coprolalia. Externally triggered inner speech has been proposed by the author to be represented by silent reading. In this setting, loss of silent reading can be regarded as the equivalent of a loss of control of the verbal utterance of the inner speech.

In the present paper, a loss of control of inner speech is suggested as partly involved in two cases of Gilles de la Tourette's syndrome with coprolalia. Two adult patients with a diagnosis of Gilles de la Tourette's syndrome since age 7 and 10, respectively, have been asked to comment on their present or previous abilities to read silently. The first case never silent read as a child while the second case read silently but had a tendency to move his lips.

The frequency of observed difficulties in silent reading is likely to be a function of the age at which the subject is asked about such difficulties. Nevertheless, theoretical arguments are presented in this part of the paper which suggest that silent reading, considered as a way to challenge the control of inner speech, has been variably impaired at different stages of the disease. The author speculates that the key role of prefrontal cortex, especially the orbito-frontal areas, in the inhibitory control of current behavior, can be responsible for the deficit in the control of inner speech. In this setting, recent functional brain imaging performed in patients with Gilles de la Tourette's syndrome showed a striking deficit in the activation of these areas during tics. It would be of great interest to address this specific question in determining the frequency of difficulties in silent reading in Gilles de la Tourette's syndrome individuals as compared to those without Gilles de la Tourette's syndrome. In this way, the so-called Stroop-test should be adequate in addressing this pivotal issue. In this well-known neuropsychological test the subject is asked to orally report the color in which the name of color has been written. The discrepancy between the color of the written word and the name of the color that have been read can challenge the ability of the subject to correctly inhibit the reading (in example the word blue ) in order to say another color (in example red , if the word blue is red colored).

Loss of silent reading observed in such patients is suggestive of the failure of the prefrontal inhibitory control on the verbal utterance of inner speech. Further research is needed to confirm these findings.