The cognitive neuroscience of memory distortion

Memory distortion occurs in the laboratory and in everyday life. This article focuses on false recognition, a common type of memory distortion in which individuals incorrectly claim to have encountered a novel object or event. By considering evidence from neuropsychology, neuroimaging, and electrophysiology, we address three questions. (1) Are there patterns of neural activity that can distinguish between true and false recognition? (2) Which brain regions contribute to false recognition? (3) Which brain regions play a role in monitoring or reducing false recognition? Neuroimaging and electrophysiological studies suggest that sensory activity is greater for true recognition compared to false recognition. Neuropsychological and neuroimaging results indicate that the hippocampus and several cortical regions contribute to false recognition. Evidence from neuropsychology, neuroimaging, and electrophysiology implicates the prefrontal cortex in retrieval monitoring that can limit the rate of false recognition.     

Electrophysiological correlates of strategic monitoring in event-based and time-based prospective memory

Prospective memory (PM) is the ability to remember to accomplish an action when a particular event occurs (i.e., event-based PM), or at a specific time (i.e., time-based PM) while performing an ongoing activity. Strategic Monitoring is one of the basic cognitive functions supporting PM tasks, and involves two mechanisms: a retrieval mode, which consists of maintaining active the intention in memory; and target checking, engaged for verifying the presence of the PM cue in the environment. The present study is aimed at providing the first evidence of event-related potentials (ERPs) associated with time-based PM, and at examining differences and commonalities in the ERPs related to Strategic Monitoring mechanisms between event- and time-based PM tasks.The addition of an event-based or a time-based PM task to an ongoing activity led to a similar sustained positive modulation of the ERPs in the ongoing trials, mainly expressed over prefrontal and frontal regions. This modulation might index the retrieval mode mechanism, similarly engaged in the two PM tasks. On the other hand, two further ERP modulations were shown specifically in an event-based PM task. An increased positivity was shown at 400-600 ms post-stimulus over occipital and parietal regions, and might be related to target checking. Moreover, an early modulation at 130-180 ms post-stimulus seems to reflect the recruitment of attentional resources for being ready to respond to the event-based PM cue. This latter modulation suggests the existence of a third mechanism specific for the event-based PM; that is, the "readiness mode".     

Properties of lung parenchyma in distortion.

This study offers a basis for evaluating and developing models of stress-strain behavior of the lung in distortion. Tensile forces were applied along three axes to cubes of dog lung parenchyma. With axially symmetrical force-loading, expansion was reasonably symmetrical and pressure-volume relationships were reasonably conventional in range, hysteresis, and time-dependent behavior. When the force load was changed on one axis only, that axis appeared more compliant than it did during symmetrical loading and the other axes changed length in the opposite sign. Similar distortion was apparent at the alveolar level. Data for five specimens over a range of applied loads are filed with the National Auxiliary Publications Service; graphical examples are presented herein. Relationship among the compliances for symmetrical and asymmetrical loadings were consistent with elastic theory. We derived the elastic coefficients, bulk and Young's moduli, and Poisson's ratio from the data. Poison's ratio was about 0.30 in air-filled specimens, but was lower (0.16-0.24) and increases with stress in saline-filled specimens.     

Emotional memory and psychopathology.

A leading model for studying how the brain forms memories about unpleasant experiences is fear conditioning. A cumulative body of work has identified major components of the neural system mediating this form of learning. The pathways involve transmission of sensory information from processing areas in the thalamus and cortex to the amygdala. The amygdala''s lateral nucleus receives and integrates the sensory inputs from the thalamic and cortical areas, and the central nucleus provides the interface with motor systems controlling specific fear responses in various modalities (behavioural, autonomic, endocrine). Internal connections within the amygdala allow the lateral and central nuclei to communicate. Recent studies have begun to identify some sites of plasticity in the circuitry and the cellular mechanisms involved in fear conditioning. Through studies of fear conditioning, our understanding of emotional memory is being taken to the level of cells and synapses in the brain. Advances in understanding emotional memory hold out the possibility that emotional disorders may be better defined and treatment improved.     

Neurohypophyseal principles and memory.

The neurohypophyseal hormones vasopressin and oxytocin modulate memory processes. Vasopressin facilitates, while oxytocin attenuates memory consolidation and retrieval. These influences are located in different regions of the molecules. Thus, the neurohypophyseal hormones act as precursor molecules for neuropeptides involved in memory processes. The covalent ring structures of both vasopressin and oxytocin mainly affect consolidation; the linear parts, retrieval processes; while nearly the whole oxytocin or vasotocin molecule is needed for attenuation of consolidation and retrieval. Regional studies, utilizing microdissection techniques in combination with a sensitive radioenzymatic catecholamine assay, revealed a distinct pattern of effects on cerebral alpha-methyl-p-tyrosine methylester-induced catecholamine disappearance following intraventricular vasopressin administration in limbic midbrain structures. In situations in which the amount of bioavailable vasopressin in the brain is absent, as is the case in the Brattleboro rat with hereditary diabetes insipidus, or neutralized in normal Wistar rats following the intraventricular administration of antivasopressin serum, regional catecholamine disappearance in most cases is altered in a direction opposite to that observed after intracerebroventricular vasopressin administration. These results indicate that vasopressin modulates memory processes by modulation of neurotransmission in distinct catecholamine systems. Recent experiments suggest that the influence of vasopressin on memory consolidation is mediated by the dorsal noradrenergic bundle via terminal regions of this bundle.     

Fas-acting memory.

Genetic and behavioral analysis points to a role for fasciclin II in controlling odor memory and alcohol sensitivity in Drosophila.     

Population dynamics under parasitic sex ratio distortion.

We analyse the population dynamic effects of sex ratio distortion by vertically transmitted, feminizing parasites. We show that, for diploid hosts, sex ratio distortion may lead to extinction as males become too rare to maintain the host population through reproduction. Feminizers can magnify Allee effects, broadening the range of conditions leading to extinction of small populations. Depending on male mating constraints and strength of density dependence, feminizers may either increase or decrease the equilibrium host density. Under conditions leading to deterministic host extinction, stochastic elimination of the parasite may allow the host population to recover. Hence, infection by parasitic sex ratio distorters may be transient in finite populations. We consider the implications of this process for parasite prevalence, host population regulation, and sex ratio evolution.     

ABO segregation distortion in Visakhapatnam, India.

Distortions in mother-infant, mother-child and father-child segregation for the ABO system as well as in the sex of offspring are described in a sample from a maternity service and from families of Visakhapatnam, India. Some distortions follow the expected fetomaternal incompatibility depression, others the expected feto-maternal induction of tolerance, and some remain unexplained. A differential action of selective factors on male and female fetuses, infants and children was also found, but no hypothesis could be postulated to explain it. The mother-infant matrix was found to be different from the mother-child matrix probably due to the inclusion of the reproductive time only in the mother-infant matrix. Unexpectedly, father-child segregation distortions were also found.     

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.     

X-chromosome inactivation and cell memory.

Mammalian X-chromosome inactivation is an excellent example of the faithful maintenance of a determined chromosomal state. As such, it may provide insight into the mechanisms for cell memory, defined as the faithful maintenance of a determined state in clonally derived progeny cells. We review here the aspects of X-chromosome inactivation that are relevant to cell memory and discuss the various molecular mechanisms that have been proposed to explain its occurrence, with emphasis on DNA methylation and a recently proposed mechanism that depends on the timing of replication.     

Chest wall distortion and discharge of pulmonary slowly adapting receptors.

We assessed the effects of chest wall distortion, changes in lung volume, and abolition of airway smooth muscle tone on the discharge patterns of 92 pulmonary slowly adapting receptors (SAR) in decerebrate, spontaneously breathing cats. Distortion resulted from their inspiratory efforts against an occluded airway at functional residual capacity and at increased end-expiratory lung volumes. Approximately 40% of SAR increased discharge frequencies during occlusions. Modulation of SAR discharge during occlusions persisted after administration of atropine to eliminate airway smooth muscle tone. Phasic modulation of SAR discharge was eliminated during no-inflation tests after paralyzing the cats and ventilating them on a cycle-triggered pump. We conclude 1) parasympathetic modulation of airway smooth muscle tone makes no obvious contribution to SAR discharge in spontaneously breathing cats; 2) the no-inflation test (withholding of lung inflation during neural inspiration) in paralyzed and ventilated cats is a valid test for the presence of projections from SAR to medullary respiratory neurons; and 3) in the absence of tidal volume changes, distortion stimulates some SAR. Sensory feedback from receptors in the lung, not just those in the chest wall, may therefore provide information about abnormal chest wall configurations.