The connectional anatomy of visual mental imagery: evidence from a patient with left occipito-temporal damage.

Most of us can use our "mind's eye" to mentally visualize things that are not in our direct line of sight, an ability known as visual mental imagery. Extensive left temporal damage can impair patients' visual mental imagery experience, but the critical locus of lesion is unknown. Our recent meta-analysis of 27 fMRI studies of visual mental imagery highlighted a well-delimited region in the left lateral midfusiform gyrus, which was consistently activated during visual mental imagery, and which we called the Fusiform Imagery Node (FIN). Here, we describe the connectional anatomy of FIN in neurotypical participants and in RDS, a right-handed patient with an extensive occipito-temporal stroke in the left hemisphere. The stroke provoked right homonymous hemianopia, alexia without agraphia, and color anomia. Despite these deficits, RDS had normal subjective experience of visual mental imagery and reasonably preserved behavioral performance on tests of visual mental imagery of object shape, object color, letters, faces, and spatial relationships. We found that the FIN was spared by the lesion. We then assessed the connectional anatomy of the FIN in the MNI space and in the patient's native space, by visualizing the fibers of the inferior longitudinal fasciculus (ILF) and of the arcuate fasciculus (AF) passing through the FIN. In both spaces, the ILF connected the FIN with the anterior temporal lobe, and the AF linked it with frontal regions. Our evidence is consistent with the hypothesis that the FIN is a node of a brain network dedicated to voluntary visual mental imagery. The FIN could act as a bridge between visual information and semantic knowledge processed in the anterior temporal lobe and in the language circuits.

Universal and language-specific sublexical cues in speech perception: a novel electroencephalography-lesion approach.

SEE CAPPA DOI101093/BRAIN/AWW090 FOR A SCIENTIFIC COMMENTARY ON THIS ARTICLE : The phonological structure of speech supports the highly automatic mapping of sound to meaning. While it is uncontroversial that phonotactic knowledge acts upon lexical access, it is unclear at what stage these combinatorial rules, governing phonological well-formedness in a given language, shape speech comprehension. Moreover few studies have investigated the neuronal network affording this important step in speech comprehension. Therefore we asked 70 participants-half of whom suffered from a chronic left hemispheric lesion-to listen to 252 different monosyllabic pseudowords. The material models universal preferences of phonotactic well-formedness by including naturally spoken pseudowords and digitally reversed exemplars. The latter partially violate phonological structure of all human speech and are rich in universally dispreferred phoneme sequences while preserving basic auditory parameters. Language-specific constraints were modelled in that half of the naturally spoken pseudowords complied with the phonotactics of the native language of the monolingual participants (German) while the other half did not. To ensure universal well-formedness and naturalness, the latter stimuli comply with Slovak phonotactics and all stimuli were produced by an early bilingual speaker. To maximally attenuate lexico-semantic influences, transparent pseudowords were avoided and participants had to detect immediate repetitions, a task orthogonal to the contrasts of interest. The results show that phonological 'well-formedness' modulates implicit processing of speech at different levels: universally dispreferred phonological structure elicits early, medium and late latency differences in the evoked potential. On the contrary, the language-specific phonotactic contrast selectively modulates a medium latency component of the event-related potentials around 400 ms. Using a novel event-related potential-lesion approach allowed us to furthermore supply first evidence that implicit processing of these different phonotactic levels relies on partially separable brain areas in the left hemisphere: contrasting forward to reversed speech the approach delineated an area comprising supramarginal and angular gyri. Conversely, the contrast between legal versus illegal phonotactics consistently projected to anterior and middle portions of the middle temporal and superior temporal gyri. Our data support the notion that phonological structure acts on different stages of phonologically and lexically driven steps of speech comprehension. In the context of previous work we propose context-dependent sensitivity to different levels of phonotactic well-formedness.