Subtitled speech: the neural mechanisms of ticker-tape synaesthesia.

Reading acquisition modifies areas of the brain associated with vision, with language, and their connections. Those changes enable reciprocal translation between orthography, and word sounds and meaning. Individual variability in the pre-existing cerebral substrate contributes to the range of eventual reading abilities, extending to atypical developmental patterns, including dyslexia and reading-related synesthesias. The present study is devoted to the little-studied but highly informative ticker-tape synesthesia (TTS), in which speech perception triggers the vivid and irrepressible perception of words in their written form in the mind's eye. We scanned a group of 17 synesthetes and 17 matched controls with functional MRI, while they listened to spoken sentences, words, numbers, or pseudowords (Experiment 1), viewed images and written words (Experiment 2), and were at rest (Experiment 3). First, we found direct correlates of the TTS phenomenon: during speech perception, as TTS was active, synesthetes showed over-activation of left perisylvian regions supporting phonology, and of the occipitotemporal Visual Word Form Area (VWFA), where orthography is represented. Second, we brought support to the hypothesis that TTS results from atypical relationships between spoken and written language processing: the TTS-related regions overlap closely with cortices activated during reading, and the overlap of speech-related and reading-related areas is larger in synesthetes than in controls. Furthermore the regions over-activated in TTS overlap with regions under-activated in dyslexia. Third, during resting state, that is in the absence of current TTS, synesthetes showed increased functional connectivity between left prefrontal and bilateral occipital regions. This pattern may reflect a lowered threshold for conscious access to visual mental contents, and may implement a non-specific predisposition to all synesthesias with a visual content. Those data provide a rich and coherent account of TTS as a non-detrimental developmental condition created by the interaction of reading acquisition with an atypical cerebral substrate.

Are we aware of neural activity in primary visual cortex? A neuropsychological case study.

OBJECTIVE: According to a seminal hypothesis stated by Crick and Koch in 1995, one is not aware of neural activity in primary visual cortex (V1) because this region lacks reciprocal connections with prefrontal cortex (PFC). METHODS: We provide here a neuropsychological illustration of this hypothesis in a patient with a very rare form of cortical blindness: ventral and dorsal cortical pathways were lesioned bilaterally while V1 areas were partially preserved. RESULTS: Visual stimuli escaped conscious perception but still activated V1 regions that were functionally disconnected from PFC. INTERPRETATION: These results are consistent with the hypothesis of a causal role of PFC in visual awareness.

The advantage of being a synesthete: The behavioral benefits of ticker-tape synesthesia.

As first described by Francis Galton, some persons perceive vividly and automatically in their mind's eye the written form of words that they are hearing. This phenomenon, labeled ticker-tape synesthesia (TTS), is thought to reflect an abnormally strong influence of speech processing in language areas on to orthographic representations in the visual cortex. Considering the relevance of TTS for the study of reading acquisition, we looked for objective behavioral advantages or impairments in 22 synesthetes, as compared to 22 matched control participants. In three auditory tasks relying on orthographic working memory (letters counting, backward spelling, and letter shape decision), we predicted and observed better performance in synesthetes than in controls. In two visual tasks (lexical decision and letter decision) with a concurrent auditory stimulation, we predicted that synesthetes should suffer from a larger interference by irrelevant speech than controls, but eventually found no difference between the groups. Those results, which we discuss in relation to orthographic processing, mental imagery, and working memory, promote TTS from pure subjectivity to an experimentally measurable phenomenon.

A single case neuroimaging study of tickertape synesthesia.

Reading acquisition is enabled by deep changes in the brain's visual system and language areas, and in the links subtending their collaboration. Disruption of those plastic processes commonly results in developmental dyslexia. However, atypical development of reading mechanisms may occasionally result in ticker-tape synesthesia (TTS), a condition described by Francis Galton in 1883 wherein individuals "see mentally in print every word that is uttered (…) as from a long imaginary strip of paper". While reading is the bottom-up translation of letters into speech, TTS may be viewed as its opposite, the top-down translation of speech into internally visualized letters. In a series of functional MRI experiments, we studied MK, a man with TTS. We showed that a set of left-hemispheric areas were more active in MK than in controls during the perception of normal than reversed speech, including frontoparietal areas involved in speech processing, and the Visual Word Form Area, an occipitotemporal region subtending orthography. Those areas were identical to those involved in reading, supporting the construal of TTS as upended reading. Using dynamic causal modeling, we further showed that, parallel to reading, TTS induced by spoken words and pseudowords relied on top-down flow of information along distinct lexical and phonological routes, involving the middle temporal and supramarginal gyri, respectively. Future studies of TTS should shed new light on the neurodevelopmental mechanisms of reading acquisition, their variability and their disorders.

Subtitled speech: Phenomenology of tickertape synesthesia.

With effort, most literate persons can conjure more or less vague visual mental images of the written form of words they are hearing, an ability afforded by the links between sounds, meaning, and letters. However, as first reported by Francis Galton, persons with ticker-tape synesthesia (TTS) automatically perceive in their mind's eye accurate and vivid images of the written form of all utterances which they are hearing. We propose that TTS results from an atypical setup of the brain reading system, with an increased top-down influence of phonology on orthography. As a first descriptive step towards a deeper understanding of TTS, we identified 26 persons with TTS. Participants had to answer to a questionnaire aiming to describe the phenomenology of TTS along multiple dimensions, including visual and temporal features, triggering stimuli, voluntary control, interference with language processing, etc. We also assessed the synesthetic percepts elicited experimentally by auditory stimuli such as non-speech sounds, pseudowords, and words with various types of correspondence between sounds and letters. We discuss the potential cerebral substrates of those features, argue that TTS may provide a unique window in the mechanisms of written language processing and acquisition, and propose an agenda for future research.

Charcot-Marie-Tooth disease misdiagnosed as chronic inflammatory demyelinating polyradiculoneuropathy: An international multicentric retrospective study.

BACKGROUND AND PURPOSE: Charcot-Marie-Tooth (CMT) disease, an untreatable hereditary polyneuropathy, may mimic chronic inflammatory demyelinating polyradiculoneuropathy (CIDP), a treatable neuropathy. METHODS: In this retrospective study, we analyzed the characteristics of CMT patients misdiagnosed as CIDP at 16 university hospitals in three countries, compared these patients with a reference group of CIDP patients, and estimated the cost of misdiagnosis. RESULTS: Among 1104 CIDP cases, we identified 35 CMT patients misdiagnosed as CIDP (3.2%). All were initially diagnosed with definite or probable CIDP (European Federation of Neurological Societies/Peripheral Nerve Society criteria), and mutations in PMP22, MPZ, and 10 other CMT genes were found in 34%, 31%, and 35% of cases, respectively. In comparison with a reference group of 35 CIDP patients, CMT patients were younger (median age at disease onset = 39 vs. 56 years) and more frequently had motor weakness at disease onset (80% vs. 29%), hearing loss (14% vs. 0%), normal brachial plexus imaging (70% vs. 40%), lower cerebrospinal fluid protein content (median = 0.5 vs. 0.8 g/L), and lower treatment response (20% vs. 69%). Treatment cost in these 35 misdiagnosed patients was estimated at 4.6 million euros (M€), whereas the cost of CMT genetic analysis in 1104 patients was estimated at 2.7 M€. CONCLUSIONS: In this study, 35 of 1104 (3.2%) patients initially diagnosed with CIDP had CMT. Importantly, the cost of treating these 35 misdiagnosed patients was significantly higher than the cost of performing CMT genetic analysis in 1104 patients (4.6 M€ vs. 2.7 M€), suggesting that CMT genetic investigations should be more widely used before diagnosing CIDP.

Herpes simplex encephalitis: A new type of "ICU-acquired infection"?

PURPOSE: Although it is a well-known disease, the occurrence of Herpes simplex encephalitis (HSE) during a hospital stay may render the diagnosis particularly challenging. The objective of this report is to alert clinicians about the diagnostic pitfalls arising from hospital-developed HSE. MATERIALS AND METHODS: Clinical observation of one patient. CASE REPORT: An 87-year-old male was admitted to the Intensive Care Unit (ICU) because of respiratory failure due to an exacerbation of myasthenia gravis. After corticoids and azathioprine treatment, his clinical condition improved, allowing weaning from mechanical ventilation. One month after admission, while still hospitalized in the ICU, the patient developed fever and confusion. In the context of confounding factors, HSE was not suspected before a convulsive status epilepticus occurred, resulting in a significant delay in treatment. Diagnosis was confirmed by PCR-analysis in the cerebrospinal fluid. Serological status confirmed reactivation of prior herpes simplex infection. The patient died one week after the onset of confusion. CONCLUSIONS: Hospital-"acquired" HSE must be suspected in case of new neurologic symptoms associated with fever, even in ICU-hospitalized patients. The diagnosis is made even more difficult by nonspecific symptoms due to previous diseases, leading to an even more severe prognosis in those vulnerable patients.