Robyn Westmacott

Functional neuroanatomy of remote episodic, semantic and spatial memory: a unified account based on multiple trace theory.

We review lesion and neuroimaging evidence on the role of the hippocampus, and other structures, in retention and retrieval of recent and remote memories. We examine episodic, semantic and spatial memory, and show that important distinctions exist among different types of these memories and the structures that mediate them. We argue that retention and retrieval of detailed, vivid autobiographical memories depend on the hippocampal system no matter how long ago they were acquired. Semantic memories, on the other hand, benefit from hippocampal contribution for some time before they can be retrieved independently of the hippocampus. Even semantic memories, however, can have episodic elements associated with them that continue to depend on the hippocampus. Likewise, we distinguish between experientially detailed spatial memories (akin to episodic memory) and more schematic memories (akin to semantic memory) that are sufficient for navigation but not for re‐experiencing the environment in which they were acquired. Like their episodic and semantic counterparts, the former type of spatial memory is dependent on the hippocampus no matter how long ago it was acquired, whereas the latter can survive independently of the hippocampus and is represented in extra‐hippocampal structures. In short, the evidence reviewed suggests strongly that the function of the hippocampus (and possibly that of related limbic structures) is to help encode, retain, and retrieve experiences, no matter how long ago the events comprising the experience occurred, and no matter whether the memories are episodic or spatial. We conclude that the evidence favours a multiple trace theory (MTT) of memory over two other models: (1) traditional consolidation models which posit that the hippocampus is a time‐limited memory structure for all forms of memory; and (2) versions of cognitive map theory which posit that the hippocampus is needed for representing all forms of allocentric space in memory.

The contribution of autobiographical significance to semantic memory.

We examined the importance of autobiographical significance (AS) in the representation and organization of semantic memory by examining which famous people are most likely to be associated with specific personal memories and whether or not this AS can be distinguished from other factors, such as familiarity. Norming studies with 45-to 55-year-old and 65-to 80-year-old participants suggested that AS is distinct from familiarity and that it interacts closely with emotional salience. Furthermore, in a set of experiments, we tested the hypothesis that AS is an important organizing principle in long-term episodic and semantic memory by contrasting performances on tests of recall, recognition, fame judgment, and speeded reading for famous names judged to be of either high or low personal relevance. Participants demonstrated a performance advantage (i.e., enhanced memory and faster responding) for autobiographically significant famous names, regardless of whether their own judgments or others’ judgments were used to classify the names. The implications of these findings for models of semantic memory are discussed.

The contribution of autobiographical significance to semantic memory: evidence from Alzheimer's disease, semantic dementia, and amnesia.

In a previous study [Memory Cognit., in press], we demonstrated that some semantic concepts are more likely than others to be associated with specific personal memories, and that this autobiographical significance gives these concepts special status in long-term memory. In this paper, we explore the possible neural correlates of autobiographically significant semantic knowledge and examine whether or not autobiographical significance is a factor in determining patterns of semantic memory loss caused by brain damage. Using famous names that were rated on various attributes, including autobiographical significance, by control participants in a norming study [Memory Cognit., in press], we found that semantic dementia (SD) patients were more likely to recognize, identify and remember autobiographically significant episodes involving famous names that were rated high in autobiographical significance as compared to equally familiar names that were rated low. By contrast, people with Alzheimers disease (AD) and people with medial temporal lobe (MTL) amnesia did not exhibit this preference for names rated high in autobiographical significance. Furthermore, in tests of free recall, recognition, fame judgment and speeded reading, semantic dementia patients demonstrated a performance advantage for autobiographically significant famous names, whereas the other patient groups did not. These findings suggest a critical role for medial temporal regions in the mediation of autobiographical memory and the interaction between personal experience and semantic memory. Theoretical implications are discussed.

Different Patterns of Autobiographical Memory Loss in Semantic Dementia and Medial Temporal Lobe Amnesia: a Challenge to Consolidation Theory

Temporally graded retrograde memory loss, with a disproportionate impairment of recent relative to remote memories, is considered a hallmark of medial temporal lobe amnesia. According to consolidation theory, the hippocampal complex, which includes the hippocampal formation, parahippocampal gyrus, the entorhinal and perirhinal cortex, plays a time-limited role in memory, needed only until consolidation in the neocortex is complete (Squire, Psychological Review 1992; 99: 195–231). Recent support for this theory comes from findings of a reverse gradient in people with semantic dementia with neocortical degeneration but a relatively preserved hippocampal complex (Hodges and Graham, Neuropsychologia 1998; 36: 803–25). Consolidation theory is challenged by evidence that remote autobiographical memory is not always spared in amnesia (Nadel and Moscovitch, Current Opinion in Neurobiology 1997; 7: 217–27) and that semantic memory becomes highly personalized in semantic dementia (Snowden et al., Memory 1995; 3: 225–46). According to Nadel and Moscovitch, the hippocampal complex is needed to retain and retrieve detailed memories of autobiographical episodes no matter how old they are. To test consolidation theory against the opposing view, we investigated the role of the hippocampal complex in recent and remote autobiographical and personal semantic memory by contrasting the memory of a semantic dementia patient, EL, with that of an amnesic patient, KG, using family photographs as recall cues. KG demonstrated a complete loss of autobiographical episodes with a sparing of autobiographical facts; EL demonstrated well-preserved memory for episodes with a reverse gradient for personally relevant names. The influence of autobiographical significance on memory for names of public figures was examined further by comparing the effect that familiarity and recollection had on recognition of names of famous people and famous places. EL’s memory was influenced by autobiographical significance, whereas KC’s was not. We propose that the hippocampal complex plays a permanent role in the storage and retrieval of autobiographical episodes and that autobiographical significance may affect semantic representations.

Late Emergence of Cognitive Deficits After Unilateral Neonatal Stroke

Background and Purpose— Neonatal arterial ischemic stroke (AIS) affects a surprisingly large number of children each year, yet little is known about the long-term neuropsychological implications. Methods— Using age-appropriate Wechsler scales of intellectual ability, this longitudinal study examined 26 children with a history of acutely diagnosed unilateral neonatal AIS as preschoolers (3 years 6 months to 5 years 11 months) and again as grade-school students (6 years 1 month to 12 years 5 months), and contrasted performance with the normative sample of the test. Results— As preschoolers, patients’ performance did not differ from the normative sample for Full Scale IQ, Verbal IQ, or Performance IQ, and there were no significant differences associated with infarct laterality. As school-age children, performance was significantly lower than the normative sample for Full Scale IQ Working Memory and Processing Speed, but not for Verbal IQ or Performance IQ. Contrasts between Time 1 and Time 2 revealed a significant decline in Full Scale IQ, which reflected emerging deficits in nonverbal reasoning, working memory, and processing speed. Individual subject analyses revealed that 69% of the children showed significant declines in 1 or more IQ index measures. We found no significant differences in cognitive performance associated with lesion laterality, though males performed more poorly than females on several cognitive measures at Time 2. Conclusions— These findings suggest that children with unilateral neonatal stroke, particularly males, are at increased risk for emerging deficits in higher-level cognitive skills during the school years. Continued follow-up of these children is needed, even those with no apparent deficits as toddlers or preschoolers.

Cognitive outcome following unilateral arterial ischaemic stroke in childhood: effects of age at stroke and lesion location

Aim  Plasticity in the developing brain is a controversial issue. Although language and motor function often recover remarkably well following early brain injury, recent evidence suggests that damage to the developing brain results in significant long‐term neuropsychological impairment. Our aim was to investigate the relationship among age at injury, lesion location and intellectual outcome.

Predictors of Quality of Life in Pediatric Survivors of Arterial Ischemic Stroke and Cerebral Sinovenous Thrombosis

Predictors of quality of life can define potentially modifiable factors to increase favorable outcomes after pediatric stroke. Quality of life was measured using the Centre for Health Promotion’s Quality of Life Profile (CHP-QOL) in 112 children surviving arterial ischemic stroke or cerebral sinovenous thrombosis at mean 3 years after stroke. Overall quality of life was poor in 17.8% children despite mean scores (3.52) in the “adequate” range. Quality of life related to school and play was most problematic and that related to physical and home environment was least problematic. Female gender, cerebral sinovenous thrombosis stroke, and older age at testing predicted reduced overall and domain-specific quality of life (P < .05), whereas neurological outcome and family socioeconomic status did not. Cognitive/behavioral deficit and low Verbal IQ adversely affected socialization and quality of life, especially among older children and females. Altered cognition/behavior has a major impact on quality of life after pediatric stroke. Implementation of ameliorative strategies warrants further study.

Temporally graded semantic memory loss in Alzheimer's disease: Cross-sectional and longitudinal studies

Abstract Semantic knowledge of famous names and words that entered popular North American culture at different times in the 20th century was examined in 16 patients with mild-to-moderate Alzheimers disease (AD), 12 of whom were re-tested 1 year later. All patients showed evidence of temporally graded memory loss, with names and words from the remote past being relatively better preserved than recent names and words. There was considerable between-patient variability with respect to severity of semantic impairment. Most patients exhibited losses extending back 30-40 years; however, two mildly impaired (MMSE >28) patients showed deficits restricted to the last 10-15 years. At the 1-year follow-up, patients not only exhibited more severe deficits overall, but the temporally graded period of loss extended further back in time, suggesting that this deficit reflects a loss of previously intact knowledge and not merely faulty encoding or lack of exposure to the material. The extensive period of graded semantic loss exhibited by most patients contrasts with the temporally limited retrograde semantic loss typical of medial temporal lobe amnesia. We propose that short periods of temporally graded semantic memory loss can be explained by damage to medial temporal structures, but that extensive periods of graded loss occur only with additional damage to neocortical tissue. This pattern contrasts with that of autobiographical memory loss, which is often ungraded and extends for the persons entire lifetime, even when damage is restricted to the medial temporal lobes.

Determinants of cognitive outcomes of perinatal and childhood stroke: A review

Our understanding of cognitive and behavioral outcomes of perinatal and childhood stroke is rapidly evolving. A current understanding of cognitive outcomes following pediatric stroke can inform prognosis and direct interventions and our understanding of plasticity in the developing brain. However, our understanding of these outcomes has been hampered by the notable heterogeneity that exists amongst the pediatric stroke population, as the influences of various demographic, cognitive, neurological, etiological, and psychosocial variables preclude broad generalizations about outcomes in any one cognitive domain. We therefore aimed to conduct a detailed overview of the published literature regarding the effects of age at stroke, time since stroke, sex, etiology, lesion characteristics (i.e., location, laterality, volume), neurologic impairment, and seizures on cognitive outcomes following pediatric stroke. A key theme arising from this review is the importance of interactive effects among variables on cognitive outcomes following pediatric stroke. Interactions particularly of note include the following: (a) age at Stroke x Lesion Location; (b) Lesion Characteristics (i.e., volume, location) x Neurologic Impairment; (c) Lesion Volume x Time Since Stroke; (d) Sex x Lesion Laterality; and (e) Seizures x Time Since Stroke. Further, it appears that these relationships do not always apply uniformly across cognitive domains but, rather, are contingent upon the cognitive ability in question. Implications for future research directions are discussed.

Early cognitive outcome after neonatal stroke.

The purpose of this study was to assess the cognitive development of 27 children with nonhemorrhagic neonatal stroke (occurring within the first 28 days of life). The cognitive evaluation consisted of the Bayley Scales of Infant Development, administered at 12 and/or 24 months poststroke. Compared with the normative sample, children with neonatal stroke obtained significantly lower scores on the Bayley Psychomotor Development Index at 12 months poststroke and on the Bayley Mental and Psychomotor Development Indices at 24 months poststroke. Outcome did not differ based on stroke type or laterality of infarct. However, there was a trend toward higher scores on the Bayley Psychomotor Development Index at 24 months in the left hemisphere group compared to the right hemisphere group. Overall, children with neonatal stroke evidenced significant impairment within the first 2 years poststroke. Further research is required to confirm whether cognitive impairments in these children resolve, remain in the low-average range, or increase with development as more complex skills are learned.