Neuropsychologia
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Research has firmly established a link between recognition memory and the functional integrity of the medial temporal lobes (MTL). Dual-process models of MTL organization maintain that there is a division of labour within the MTL, with the hippocampus (HC) supporting recollective processes and perirhinal cortex (PRc) supporting familiarity assessment. An older neuropsychological literature suggested a different type of division of labour within the MTL, with left-sided structures playing a critical role in memory for verbal materials and right-sided structures being differentially involved in memory for material that cannot easily be verbalized. ⋯ We found that NB exhibited a deficit in overall recognition of aurally presented pronounceable non-words that reflected a specific impairment of familiarity assessment with preservation of recollective processes. Examination of recognition memory for visually presented abstract pictures and faces did not reveal any impairment, neither at the level of overall recognition nor, more specifically, at the level of familiarity assessment. These findings suggest that the neural mechanisms that support familiarity assessment in the temporal lobe operate in a manner that is tied to the specific stimulus class being assessed.
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Evidence from event-related potential (ERP) analyses of English spoken words suggests that the time course of English word recognition in monosyllables is cumulative. Different types of phonological competitors (i.e., rhymes and cohorts) modulate the temporal grain of ERP components differentially (Desroches, Newman, & Joanisse, 2009). The time course of Chinese monosyllabic spoken word recognition could be different from that of English due to the differences in syllable structure between the two languages (e.g., lexical tones). ⋯ In contrast to the English findings, our findings showed that the three partial mismatches (onset, rime, and tone mismatches) equally modulated the amplitudes and time courses of the N400 (a negative component that peaks about 400ms after the spoken word), whereas, the syllable mismatched words elicited an earlier and stronger N400 than the three partial mismatched words. The results shed light on the important role of syllable-level awareness in Chinese spoken word recognition and also imply that the recognition of Chinese monosyllabic words might rely more on global similarity of the whole syllable structure or syllable-based holistic processing rather than phonemic segment-based processing. We interpret the differences in spoken word processing between Chinese and English listeners as being due to morphosyllabic structural differences between the two languages.
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In humans lacunar infarcts in the mesial and anterior regions of the thalami are frequently associated with amnesic syndromes. In this review paper, we scrutinized 41 papers published between 1983 and 2009 that provided data on a total of 83 patients with the critical ischemic lesions (i.e. 17 patients with right-sided lesions, 25 with left-sided lesions and 41 with bilateral lesions). We aimed to find answers to the following questions concerning the vascular thalamic amnesia syndrome: (i) Which qualitative pattern of memory impairment (and associated cognitive and behavioral deficits) do these patients present? (ii) Which lesioned intrathalamic structures are primarily responsible for the amnesic syndrome? (iii) Are the recollection and familiarity components of declarative memory underlain by the same or by different thalamic structures? Results of the review indicate that, similar to patients with amnesic syndromes due to mesio-temporal lobe damage, patients with vascular thalamic amnesia display a prevalent deficit of declarative anterograde long-term memory, a less consistent deficit of declarative retrograde long-term memory and substantially spared short-term and implicit memory. ⋯ The presence of an amnesic syndrome in patients with thalamic lacunar infarcts is strongly predicted by involvement of the mammillo-thalamic tract, which connects the anterior nuclei complex to the hippocampus proper via the fornix and the mammillary bodies. Finally, data reported in a few single cases provide support for the hypothesis that thalamic regions connected to distinct areas of the mesio-temporal lobe play differential roles in recollection and familiarity processes. The mammillo-thalamic tract/anterior nuclei axis seems primarily implicated in recollective processes, whereas the ventroamygdalofugal pathway/medio-dorsal axis primarily underlies familiarity processes.
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Glucose enhances memory in a variety of species. In humans, glucose administration enhances episodic memory encoding, although little is known regarding the neural mechanisms underlying these effects. Here we examined whether elevating blood glucose would enhance functional MRI (fMRI) activation and connectivity in brain regions associated with episodic memory encoding and whether these effects would differ depending on the emotional valence of the material. ⋯ Finally, glucose substantially increased functional connectivity between the hippocampus and amygdala and a network of regions previously implicated in successful episodic memory encoding. These findings fit with evidence from nonhuman animals indicating glucose modulates memory by selectively enhancing neural activity in brain regions engaged during memory tasks. Our results highlight the modulatory effects of glucose and the importance of examining both regional changes in activity and functional connectivity to fully characterize the effects of glucose on brain function and memory.
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Decision-making is a complex process that requires the orchestration of multiple neural systems. For example, decision-making is believed to involve areas of the brain involved in emotion (e.g., amygdala, ventromedial prefrontal cortex) and memory (e.g., hippocampus, dorsolateral prefrontal cortex). In this article, we will present findings related to the amygdala's role in decision-making, and differentiate the contributions of the amygdala from those of other structurally and functionally connected neural regions. ⋯ Studies using laboratory decision-making tests have found deficient decision-making in patients with bilateral amygdala damage, which resembles their real-world difficulties with decision-making. Additionally, we have found evidence for an interaction between sex and laterality of amygdala functioning, such that unilateral damage to the right amygdala results in greater deficits in decision-making and social behavior in men, while left amygdala damage seems to be more detrimental for women. We have posited that the amygdala is part of an "impulsive," habit type system that triggers emotional responses to immediate outcomes.