‘I saw the words right from your mouth’: An unusual case of synaesthesia

To the Editor

We present a unique case of synaesthesia associated with an arachnoid cyst in the temporal lobe. Synaesthesia is the involuntary experience of feeling one sensation in direct response to a different sensory stimulus. Approximately 1% of the population has synaesthesia (Sagiv and Ward, 2006). Arachnoid cysts are benign, cerebrospinal fluid-containing lesions accounting for 1% of lesions occupying the intracranial space (da Silva et al., 2007).

Mr AB is a 39-year-old man of Serbian background. He first described ticker-tape synaesthesia at age 6 when he would see words spoken to him as ‘letters on a chalkboard’ or ‘subtitles in a movie’. He could see the spoken words as soon as he heard them. The experience became overwhelming if he heard multiple voices at the same time, where the visualised letters tended to jumble. The words he saw were in Cyrillic, the script of his native language. Mr AB did not experience any other form of synaesthesia and there was no family history of synaesthesia.

He first presented to hospital at age 16 with persecutory delusions.  As part of the initial organic workup, a magnetic resonance imaging scan defined a 3.4 × 3.6 × 3 cm arachnoid cyst in the left cranial fossa with mass effect on the left temporal lobe. A positron emission tomography scan demonstrated reduced perfusion in left temporal lobe. Neurological examination was normal. Neurosurgical opinion was subsequently sought regarding the removal of the arachnoid cyst, but consensus was that the cyst should be conservatively managed.

Multiple subsequent hospitalisations, due to recurrent psychotic episodes, took place. However, Mr AB’s synaesthesia had steadily increased in intensity over the years, irrespective of the intensity of psychotic symptoms or treatment with antipsychotic medication.

Synaesthesia has attracted much research interest. However, this particular form of synaesthetic experience has only been described once in the literature as ticker-tape synaesthesia (Cytowic and Eagleman, 2009). Of interest in our patient is evidence of temporal lobe pathology related to hypoperfusion due to the mass effect of the arachnoid cyst on the left temporal lobe. The progressive increase in intensity of Mr AB’s synaesthesia may suggest that the arachnoid cyst is growing in size. We speculate that temporal lobe pathology is associated with his rare synaesthetic experience, in addition to his psychotic symptoms. Synaesthesia can originate from the temporal lobe, especially in the case of temporal lobe epilepsy (Cytowic, 2002). The neurophysiological mechanism of synaesthesia, however, is mostly unknown. It has been postulated that cross-activation of the perceptual areas due to anomalous processing in the perceptual association areas is the mechanism behind synaesthesia (Hubbard and Ramachandran, 2005). Another hypothesis is that cross-wiring networks fail to disconnect during neurodevelopment (Hubbard and Ramachandran, 2005).

In summary, this case report is unique in describing a rare synaesthetic experience associated with a structural lesion compressing the left temporal lobe. Our case report therefore demonstrates the potential importance of the temporal lobe in contributing to synaesthesia. It would be of particular research interest to confirm if synaesthesia is more prevalent in patients with chronic psychosis compared to the general population given that one of the core features of schizophrenia relates to perceptual disturbance.