Neuropsychologia
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Patients with postchiasmatic visual field defects often show a contralesional bias towards the scotoma in line bisection or when indicating their visual subjective straight ahead (VSSA). Recent evidence suggests a retinotopic misrepresentation of visual space in patients with homonymous quadrantanopia (HQ). We therefore assessed in the present study whether patients with HQ show an oblique shift of their VSSA towards their scotoma, in addition to the known bias in horizontal line bisection. ⋯ All 15 patients with HQ showed a large oblique shift of their VSSA towards the blind quadrants, while normal subjects showed no systematic left-rightward shift, but a small downward shift of the VSSA. The position of the blind spot was normal in all testable eyes of patients and control subjects, thus excluding eccentric fixation or cyclorotation of the eyes. In conclusion, our study reveals a hitherto unreported oblique spatial shift of subjective visual body orientation towards the blind quadrants in non-neglecting patients with quadranopia.
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The anterior cingulate cortex (ACC) is involved in performance monitoring and in learning from performance feedback. Recent research suggests that the feedback-related negativity (FRN), an event-related potentials (ERP) component reflecting neural activity in the ACC, codes the size of a negative prediction error when reward probabilities are varied. There is as yet no clear evidence that the FRN is also sensitive to violations of reward magnitude expectations. ⋯ In contrast, the P300 was larger for positive outcomes and showed an effect of (potential) reward magnitude independent of valence. Together with evidence from previous studies, these results show that the FRN codes negative prediction errors in the context of varying reward probabilities and magnitudes. The findings are in line with recent results based on functional neuroimaging and lend further support to the idea of a key role of the ACC in the integration of information on different aspects of performance outcomes.
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There is consensus that the left hemisphere plays a dominant role in language processing, but functional imaging studies have shown that the right as well as the left posterior inferior frontal gyri (pIFG) are activated when healthy right-handed individuals make phonological word decisions. Here we used online transcranial magnetic stimulation (TMS) to examine the functional relevance of the right pIFG for auditory and visual phonological decisions. Healthy right-handed individuals made phonological or semantic word judgements on the same set of auditorily and visually presented words while they received stereotactically guided TMS over the left, right or bilateral pIFG (n=14) or the anterior left, right or bilateral IFG (n=14). ⋯ In a follow-up experiment, the intensity threshold for delaying phonological judgements was identical for unilateral TMS of left and right pIFG. These findings indicate that an intact function of right pIFG is necessary for accurate and efficient phonological decisions in the healthy brain with no evidence that the left and right pIFG can compensate for one another during online TMS. Our findings motivate detailed studies of phonological processing in patients with acute and chronic damage of the right pIFG.
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Viewing another person's hand actions enhances excitability in an observer's left and right primary motor (M1) cortex. We aimed to determine whether viewing communicative hand actions alters this bilateral sensorimotor resonance. Using single-pulse transcranial magnetic stimulation (TMS), we measured excitability in the left and right M1 while right-handed non-signing participants observed bimanual communicative hand actions, i.e., meaningful signs in British Sign Language. ⋯ After learning the meanings of half the signs, excitability of the left, but not right, M1 was significantly enhanced. This left-lateralized enhancement of M1 excitability occurred during observation of signs with known and unknown meanings. The findings suggest that awareness of the communicative nature of another person's hand actions strengthens sensorimotor resonance in the left M1 cortex and alters hemispheric balance during action observation.
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Episodic memory, the recollection of past events in one's life, has often been considered a memory specific to humans. Recent work in a variety of species has challenged this view, and has raised important questions about the nature of episodic memory itself. ⋯ We propose that identifying episodic memory as the memory for what happened where on a specific occasion is a more encompassing definition than one that relies on information about when an event occurred. These episodic-like tasks in animals support the view that the hippocampal system is necessary for episodic memory, and that the neural substrates of episodic memory can be dissociated from those of other forms of declarative memory.