Visuospatial imagery and working memory in schizophrenia.

INTRODUCTION: The ability to form mental images that reconstruct former perceptual experiences is closely related to working memory (WM) ability. However, whereas WM deficits are established as a core feature of schizophrenia, an independent body of work suggests that mental imagery ability is enhanced in the disorder. Across two experiments we investigated mental imagery in schizophrenia and its relationship with WM. METHODS: In Experiment 1, individuals with schizophrenia (SZ: n=15) and matched controls (CO: n=14) completed a mental imagery generation and inspection task and a spatial delayed-response WM task. In Experiment 2, SZ (n=16) and CO (n=16) completed a novel version of the mental imagery task modified to increase WM maintenance demand. RESULTS: In Experiment 1, SZ demonstrated enhanced mental imagery performance, as evidenced by faster response times relative to CO, with preserved accuracy. However, enhanced mental imagery in SZ was accompanied by impaired WM as assessed by the delayed-response task. In Experiment 2, when WM maintenance load was increased, SZ no longer showed superior imagery performance. CONCLUSIONS: We found evidence for enhanced imagery manipulation in SZ despite their WM maintenance deficit. However, this imagery enhancement was abolished when WM maintenance demands were increased. This profile of enhanced imagery manipulation but impaired maintenance could be used to implement novel remediation strategies in the disorder.

Starvation-induced cleavage of the tRNA anticodon loop in Tetrahymena thermophila.

Amino acid deprivation triggers dramatic physiological responses in all organisms, altering both the synthesis and destruction of RNA and protein. Here we describe, using the ciliate Tetrahymena thermophila, a previously unidentified response to amino acid deprivation in which mature transfer RNA (tRNA) is cleaved in the anticodon loop. We observed that anticodon loop cleavage affects a small fraction of most or all tRNA sequences. Accumulation of cleaved tRNA is temporally coordinated with the morphological and metabolic changes of adaptation to starvation. The starvation-induced endonucleolytic cleavage activity targets tRNAs that have undergone maturation by 5' and 3' end processing and base modification. Curiously, the majority of cleaved tRNAs lack the 3' terminal CCA nucleotides required for aminoacylation. Starvation-induced tRNA cleavage is inhibited in the presence of essential amino acids, independent of the persistence of other starvation-induced responses. Our findings suggest that anticodon loop cleavage may reduce the accumulation of uncharged tRNAs as part of a specific response induced by amino acid starvation.