Neuropsychologia
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The properties of retrograde amnesia after damage to the hippocampus have been explicated with some success using a rat model of human medial temporal lobe amnesia. We review the results of this experimental work with rats focusing on several areas of consensus in this growing literature. We evaluate the theoretically significant hypothesis that hippocampal retrograde amnesia normally exhibits a temporal gradient, affecting recent, but sparing remote memories. ⋯ There is consistent evidence that at the time of learning the hippocampus interferes with or overshadows memory acquisition by other systems. This contributes to the breadth and severity of retrograde amnesia relative to anterograde amnesia in the rat. The fact that multiple, distributed learning episodes can overcome this overshadowing is consistent with a parallel dual-store theory or a Distributed Reinstatement Theory in which each learning episode triggers a short period of memory replay that provides a brief hippocampal-dependent systems consolidation.
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Comparative Study
How does the topic of conversation affect verbal exchange and eye gaze? A comparison between typical development and high-functioning autism.
Conversation is a primary area of difficulty for individuals with high-functioning autism (HFA) although they have unimpaired formal language abilities. This likely stems from the unstructured nature of face-to-face conversation as well as the need to coordinate other modes of communication (e.g. eye gaze) with speech. We conducted a quantitative analysis of both verbal exchange and gaze data obtained from conversations between children with HFA and an adult, compared with those of typically developing children matched on language level. ⋯ However, both the HFA and comparison groups looked significantly more to their partner's face during the interest than generic topic. Our interpretation of results across modalities is that circumscribed interests led HFA participants to be less adaptive to their partner verbally, but speaking about a highly practiced topic allowed for increased gaze to the partner. The function of this increased gaze to partner may differ for the HFA and comparison groups.
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Theory of Mind--ToM, the capacity to understand one's own and other people's mental states and to refer to them to foresee and explain the behaviour--relies upon a circumscribed neural system: the posterior end of the superior temporal sulcus (pSTS), the adjacent temporo-parietal junction (TPJ), the temporal pole (TP), the medial prefrontal cortex (mPFC) and the adjacent paracingulate cortex. To our knowledge, the neural basis of mentalizing has not yet been studied in a developmental perspective covering old age, so the aim of this work is to compare the neural basis of a specific aspect of ToM, the mindreading ability through the eyes, in healthy young and old subjects. Two groups of healthy adults (young: 25.2 years; old: 65.2 years) were submitted to an fMRI scanning while performing the Reading the Mind in the Eyes test, which requires the attribution of a mental state to the other person focussing only on the eye-gaze. ⋯ Old subjects showed a more bilateral activation of frontal areas and a stronger involvement of the linguistic components of the mirror neuron system (i.e. area 44), as compared to young. Both young and old participants activated the non-linguistic components of the mirror neuron system, such as area 6. These findings are discussed taking into account the recent literature dealing with cognitive functions during normal aging.
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Initial reports of emotion recognition in Huntington's disease (HD) found disproportionate impairments in recognising disgust. Not all subsequent studies have found this pattern, and a review of the literature to date shows that marked impairments in recognising anger are also often seen in HD. However, the majority of studies have based their conclusions on a single test of facial expression recognition. ⋯ Given work identifying different subtypes of disgust that are associated with different facial features, a second study examined the recognition of three disgust expressions that healthy participants reliably associate with unpleasant tastes, unpleasant smells, and a more general elaborated or expanded form of disgust that includes reactions to violations of moral standards. The results showed a disproportionate impairment in recognising faces associated with the expanded form, the subtype most closely aligned with anger. We conclude that the related emotions of disgust and anger associated with social disapproval are frequently impaired in HD and discuss factors that might cause one emotion to show more severe impairments than the other.
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Although the mammillary bodies were among the first brain regions to be implicated in amnesia, the functional importance of this structure for memory has been questioned over the intervening years. Recent patient studies have, however, re-established the mammillary bodies, and their projections to the anterior thalamus via the mammillothalamic tract, as being crucial for recollective memory. Complementary animal research has also made substantial advances in recent years by determining the electrophysiological, neurochemical, anatomical and functional properties of the mammillary bodies. ⋯ The mammillary bodies have traditionally been considered a hippocampal relay which is consistent with the equivalent deficits seen following lesions of the mammillary bodies or their major efferents, the mammillothalamic tract. However, recent findings suggest that the mammillary bodies may have a role in memory that is independent of their hippocampal formation afferents; instead, the ventral tegmental nucleus of Gudden could be providing critical mammillary body inputs needed to support mnemonic processes. Finally, it is now apparent that the medial and lateral mammillary nuclei should be considered separately and initial research indicates that the medial mammillary nucleus is predominantly responsible for the spatial memory deficits following mammillary body lesions in rats.