Intact memory for irrelevant information impairs perception in amnesia

Memory and perception have long been considered separate cognitive processes, and amnesia resulting from medial temporal lobe (MTL) damage is thought to reflect damage to a dedicated memory system. Recent work has questioned these views, suggesting that amnesia can result from impoverished perceptual representations in the MTL, causing an increased susceptibility to interference. Using a perceptual matching task for which fMRI implicated a specific MTL structure, the perirhinal cortex, we show that amnesics with MTL damage including the perirhinal cortex, but not those with damage limited to the hippocampus, were vulnerable to object-based perceptual interference. Importantly, when we controlled such interference, their performance recovered to normal levels. These findings challenge prevailing conceptions of amnesia, suggesting that effects of damage to specific MTL regions are better understood not in terms of damage to a dedicated declarative memory system, but in terms of impoverished representations of the stimuli those regions maintain.     

Clathrin: now you see me, now you don't!

Endocytic clathrin-coated vesicles are short-lived transport intermediates that ferry cargo macromolecules rapidly into the cell interior. Recent work from the Kirchhausen laboratory indicates that the lifetime of a coated vesicle is extremely short, and assembly of nascent coats aborts abruptly unless reinforced by additional regulatory inputs, most likely cargo capture.     

Hypnosis,memory and amnesia.

Hypnotized subjects respond to suggestions from the hypnotist for imaginative experiences involving alterations in perception and memory. Individual differences in hypnotizability are only weakly related to other forms of suggestibility. Neuropsychological speculations about hypnosis focus on the right hemisphere and/or the frontal lobes. Posthypnotic amnesia refers to subjects'' difficulty in remembering, after hypnosis, the events and experiences that transpired while they were hypnotized. Posthypnotic amnesia is not an instance of state-dependent memory, but it does seem to involve a disruption of retrieval processes similar to the functional amnesias observed in clinical dissociative disorders. Implicit memory, however, is largely spared, and may underlie subjects'' ability to recognize events that they cannot recall. Hypnotic hypermnesia refers to improved memory for past events. However, such improvements are illusory: hypermnesia suggestions increase false recollection, as well as subjects'' confidence in both true and false memories. Hypnotic age regression can be subjectively compelling, but does not involve the ablation of adult memory, or the reinstatement of childlike modes of mental functioning, or the revivification of memory. The clinical and forensic use of hypermnesia and age regression to enhance memory in patients, victims and witnesses (e.g. recovered memory therapy for child sexual abuse) should be discouraged.     

Cortical plasticity: It's all the range!

When rats learn a motor skill, synaptic potentials in the motor cortex are enhanced. A new study has revealed that this learning-induced enhancement limits further synaptic potentiation, but not synaptic depression. These findings support the view that activity-dependent synaptic plasticity is the brain's memory mechanism.     

Transient global amnesia and functional retrograde amnesia: contrasting examples of episodic memory loss.

We studied 11 patients with transient global amnesia (TGA) and ten patients with functional retrograde amnesia (FRA). Patients with TGA had a uniform clinical picture: a severe, relatively isolated amnesic syndrome that started suddenly, persisted for 4-12 h, and then gradually improved to essentially normal over the next 12-24 h. During the episode, the patients had severe anterograde amnesia for verbal and non-verbal material and retrograde amnesia that typically covered at least two decades. Thirty hours to 42 days after the episode, the patients had recovered completely and performed normally on tests of anterograde and retrograde amnesia. By contrast, patients with FRA had a sudden onset of memory problems that were characterized by severe retrograde amnesia without associated anterograde amnesia and with a clinical presentation that otherwise varied considerably. The episodes persisted from several weeks to more than two years, and some of the patients had not recovered at the time of our last contact with them. The uniform clinical picture of TGA and the variable clinical picture of FRA presumably reflect their respective neurologic (''organic'') and psychogenic (''non-organic'') aetiologies.     

Dissociations in cognitive memory: the syndrome of developmental amnesia

The dearth of studies on amnesia in children has led to the assumption that when damage to the medial temporal lobe system occurs early in life, the compensatory capacity of the immature brain rescues memory functions. An alternative view is that such damage so interferes with the development of learning and memory that it results not in selective cognitive impairments but in general mental retardation. Data will be presented to counter both of these arguments. Results obtained from a series of 11 amnesic patients with a history of hypoxic ischaemic damage sustained perinatally or during childhood indicate that regardless of age at onset of hippocampal pathology, there is a pronounced dissociation between episodic memory, which is severely impaired, and semantic memory, which is relatively preserved. A second dissociation is characterized by markedly impaired recall and relatively spared recognition leading to a distinction between recollection-based versus familiarity-based judgements. These findings are discussed in terms of the locus and extent of neuropathology associated with hypoxic ischaemic damage, the neural basis of 'remembering' versus 'knowing', and a hierarchical model of cognitive memory.     

It's all relative: Regression analysis with compositional predictors

Compositional data reside in a simplex and measure fractions or proportions of parts to a whole. Most existing regression methods for such data rely on log-ratio transformations that are inadequate or inappropriate in modeling high-dimensional data with excessive zeros and hierarchical structures. Moreover, such models usually lack a straightforward interpretation due to the interrelation between parts of a composition. We develop a novel relative-shift regression framework that directly uses proportions as predictors. The new framework provides a paradigm shift for regression analysis with compositional predictors and offers a superior interpretation of how shifting concentration between parts affects the response. New equi-sparsity and tree-guided regularization methods and an efficient smoothing proximal gradient algorithm are developed to facilitate feature aggregation and dimension reduction in regression. A unified finite-sample prediction error bound is derived for the proposed regularized estimators. We demonstrate the efficacy of the proposed methods in extensive simulation studies and a real gut microbiome study. Guided by the taxonomy of the microbiome data, the framework identifies important taxa at different taxonomic levels associated with the neurodevelopment of preterm infants.