Neuropsychologia
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Randomized Controlled Trial
Heightened motor and sensory (mirror-touch) referral induced by nerve block or topical anesthetic.
Mirror neurons allow us to covertly simulate the sensation and movement of others. If mirror neurons are sensory and motor neurons, why do we not actually feel this simulation- like "mirror-touch synesthetes"? Might afferent sensation normally inhibit mirror representations from reaching consciousness? We and others have reported heightened sensory referral to phantom limbs and temporarily anesthetized arms. ⋯ We also obtain double-blind, quantitative evidence of heightened sensory referral in healthy participants completing a mirror-touch confusion task after topical anesthetic cream is applied. We suggest that sensory and motor feedback exist in dynamic equilibrium with mirror representations; as feedback is reduced, the brain draws more upon visual information to determine- perhaps in a Bayesian manner- what to feel.
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Transcranial Direct Current Stimulation (tDCS) is a non-invasive form of brain stimulation which has been shown to induce changes in brain activity and subsequent functioning. In particular, there is a rapidly growing evidence base showing that anodal tDCS applied to the left prefrontal cortex (PFC) is able to enhance aspects of cognitive functioning, in particular working memory (WM). This has led to both excitement and concerns regarding the possibility of 'electrodoping' in order to greatly improve one's cognitive performance. ⋯ Our results showed that while active tDCS can enhance behavioural performance, with neurophysiological findings indicating improve efficiency of cognitive processing; we showed that 1 mA produced the most significant effects. These findings are somewhat unexpected as tDCS dose effects in cognitive enhancement have been shown previously in patient populations. Our results provide valuable information regarding the potential limits of tDCS induced cognitive enhancement in healthy controls, as well as providing additional insights into the possible mechanisms of action of tDCS.
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Accessing the meaning of words, objects, people and facts is a human ability, made possible thanks to semantic processing. Although studies concerning its cortical organization are proficient, the subcortical connectivity underlying this semantic network received less attention. We used intraoperative direct electrostimulation, which mimics a transient virtual lesion during brain surgery for glioma in eight awaken patients, to map the anatomical white matter substrate subserving the semantic system. ⋯ These transient disorders were highly reproducible, and concerned verbal as well as non-verbal output. Our results highlight for the first time the essential role of the left inferior fronto-occipital fascicle in multimodal (and not only in verbal) semantic processing. On the basis of these original findings, and in the lights of phylogenetic considerations regarding this fascicle, we suggest its possible implication in the monitoring of the human level of consciousness related to semantic memory, namely noetic consciousness.
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This paper describes the progressive performance of JD, a patient with semantic dementia, on acronym categorisation, recognition and reading aloud over a period of 18 months. Most acronyms have orthographic and phonological configurations that are different from English words (BBC, DVD, HIV). While some acronyms, the majority, are regularly pronounced letter by letter, others are pronounced in a more holistic, and irregular, way (NASA, AWOL). ⋯ The decline in JD's semantic system led to increasingly impaired semantic categorisation and lexical decision for acronyms relative to healthy controls. However, her accuracy for reading aloud regular acronyms (i.e. those pronounced letter by letter such as BBC) remained near ceiling while reading irregular acronyms (i.e. those pronounced as mainstream words such as NASA) demonstrated impairment. It is therefore argued that consequences of semantic impairment vary across acronym types, a finding that informs our understanding of any reading account of this growing class of words.