Contributions of nonhuman primate research to understanding the consequences of human brain injury during development

In this introductory review we first present a theoretical framework as well as a clinical perspective regarding the effects of early brain injury on the development of cognitive and behavioral functions in humans. Next, we highlight the contributions that nonhuman primate research make toward identifying some of the variables that influence long-term cognitive outcome after developmental disease, or damage. We start our review by arguing that in contrast to adult-onset injury, developmental brain insults alter the ontogenetic pattern of brain organization and circuit specialization depending on the variables of age at injury, the focality of the lesion, and the potential for reorganization. We then introduce the 2 nonhuman primate studies in this section (Kiorpes on vision; Bachevalier on cognitive memory), and highlight the relevance of their findings to our understanding of developmental conditions or injuries in humans, with the ultimate goal of improving the health and development of the young

Semantic Memory in Developmental Amnesia

Patients with developmental amnesia resulting from bilateral hippocampal atrophy associated with neonatal hypoxia-ischaemia typically show relatively preserved semantic memory and factual knowledge about the natural world despite severe impairments in episodic memory. Understanding the neural and mnemonic processes that enable this context-free semantic knowledge to be acquired throughout development without the support of the contextualised episodic memory system is a serious challenge. This review describes the clinical presentation of patients with developmental amnesia, contrasts its features with those reported for adult-onset hippocampal amnesia, and analyses the effects of variables that influence the learning of new semantic information

Little evidence for fast mapping in adults with developmental amnesia.

Cooper, Greve, and Henson (this issue) conclude that hippocampal-independent learning, as operationalised by 'fast mapping' (FM), is unlikely to facilitate learning in adults. We provide evidence from patients with Developmental Amnesia (DA), who acquire language and semantic knowledge despite early hippocampal pathology. We administered an FM paradigm to three patients with DA and controls. Patients showed no benefit of FM compared to explicit encoding. These data support the conclusion that FM is unlikely to facilitate learning in amnesia, regardless of age at onset. Hippocampal-independent learning may be possible in adults with DA, but such learning requires a prolonged consolidation period

Phonological Working Memory and FOXP2

The discovery and description of the affected members of the KE family (aKE) initiated research on how genes enable the unique human trait of speech and language. Many aspects of this genetic influence on speech-related cognitive mechanisms are still elusive, e.g. if and how cognitive processes not directly involved in speech production are affected. In the current study we investigated the effect of the FOXP2 mutation on Working Memory (WM). Half the members of the multigenerational KE family have an inherited speech-language disorder, characterised as a verbal and orofacial dyspraxia caused by a mutation of the FOXP2 gene. The core phenotype of the affected KE members (aKE) is a deficiency in repeating words, especially complex non-words, and in coordinating oromotor sequences generally. Execution of oromotor sequences and repetition of phonological sequences both require WM, but to date the aKE's memory ability in this domain has not been examined in detail. To do so we used a test series based on the Baddeley and Hitch model, which posits that the central executive (CE), important for planning and manipulating information, works in conjunction with two modality-specific components: The phonological loop (PL), specialized for processing speech-based information; and the visuospatial sketchpad (VSSP), dedicated to processing visual and spatial information. We compared WM performance related to CE, PL, and VSSP function in five aKE and 15 healthy controls (including three unaffected members of the KE family who do not have the FOXP2 mutation). The aKE scored significantly below this control group on the PL component, but not on the VSSP or CE components. Further, the aKE were impaired relative to the controls not only in motor (i.e. articulatory) output but also on the recognition-based PL subtest (word-list matching), which does not require speech production. These results suggest that the aKE's impaired phonological WM may be due to a defect in subvocal rehearsal of speech-based material, and that this defect may be due in turn to compromised speech-based representations

Alexander's disease and the story of Louise.

We describe the rare condition known as Alexander's disease or Alexander's leukodystrophy, which is essentially a childhood dementia. We then present the case of Louise Davies (we are using Louise's real name with the permission and special request of her mother), a woman who was diagnosed with this disease at the age of 5 years and is still alive at the age of 38, making her the longest known survivor of this condition. Although now severely impaired, both physically and mentally, and able to do very little, she has lived far longer than expected. We present some neuropsychological results from her childhood before measuring her decline over the past four years. We conclude by considering whether or not the diagnosis was correct and why she has lived so long

Alexander's disease and the story of Louise.

We describe the rare condition known as Alexander's disease or Alexander's leukodystrophy, which is essentially a childhood dementia. We then present the case of Louise Davies (we are using Louise's real name with the permission and special request of her mother), a woman who was diagnosed with this disease at the age of 5 years and is still alive at the age of 38, making her the longest known survivor of this condition. Although now severely impaired, both physically and mentally, and able to do very little, she has lived far longer than expected. We present some neuropsychological results from her childhood before measuring her decline over the past four years. We conclude by considering whether or not the diagnosis was correct and why she has lived so long

Scene construction in developmental amnesia: An fMRI study.

Amnesic patients with bilateral hippocampal damage sustained in adulthood are generally unable to construct scenes in their imagination. By contrast, patients with developmental amnesia (DA), where hippocampal damage was acquired early in life, have preserved performance on this task, although the reason for this sparing is unclear. One possibility is that residual function in remnant hippocampal tissue is sufficient to support basic scene construction in DA. Such a situation was found in the one amnesic patient with adult-acquired hippocampal damage (P01) who could also construct scenes. Alternatively, DA patients' scene construction might not depend on the hippocampus, perhaps being instead reliant on non-hippocampal regions and mediated by semantic knowledge. To adjudicate between these two possibilities, we examined scene construction during functional MRI (fMRI) in Jon, a well-characterised patient with DA who has previously been shown to have preserved scene construction. We found that when Jon constructed scenes he activated many of the regions known to be associated with imagining scenes in control participants including ventromedial prefrontal cortex, posterior cingulate, retrosplenial and posterior parietal cortices. Critically, however, activity was not increased in Jon's remnant hippocampal tissue. Direct comparisons with a group of control participants and patient P01, confirmed that they activated their right hippocampus more than Jon. Our results show that a type of non-hippocampal dependent scene construction is possible and occurs in DA, perhaps mediated by semantic memory, which does not appear to involve the vivid visualisation of imagined scenes

When the brain, but not the person, remembers: Cortical reinstatement is modulated by retrieval goal in developmental amnesia

Developmental amnesia (DA) is associated with early hippocampal damage and subsequent episodic amnesia emerging in childhood alongside age-appropriate development of semantic knowledge. We employed fMRI to assess whether patients with DA show evidence of 'cortical reinstatement', a neural correlate of episodic memory, despite their amnesia. At study, 23 participants (5 patients) were presented with words overlaid on a scene or a scrambled image for later recognition. Scene reinstatement was indexed by scene memory effects (greater activity for previously presented words paired with a scene rather than scrambled images) that overlapped with scene perception effects. Patients with DA demonstrated scene reinstatement effects in the parahippocampal and retrosplenial cortex that were equivalent to those shown by healthy controls. Behaviourally, however, patients with DA showed markedly impaired scene memory. The data indicate that reinstatement can occur despite hippocampal damage, but that cortical reinstatement is insufficient to support accurate memory performance. Furthermore, scene reinstatement effects were diminished during a retrieval task in which scene information was not relevant for accurate responding, indicating that strategic mnemonic processes operate normally in DA. The data suggest that cortical reinstatement of trial-specific contextual information is decoupled from the experience of recollection in the presence of severe hippocampal atrophy

The Pair Test: A computerised measure of learning and memory

There is increasing interest in the assessment of learning and memory in typically developing children as well as in children with neurodevelopmental disorders. However, neuropsychological assessments have been hampered by the dearth of standardised tests that enable direct comparison between distinct memory processes or between types of stimulus materials. We developed a tablet-based paired-associate learning paradigm, the Pair Test, based on neurocognitive models of learning and memory. The aims are to (i) establish the utility of this novel memory tool for use with children across a wide age range, and (ii) examine test validity, reliability and reproducibility of the construct. The convergent validity of the test was found to be adequate, and higher test reliability was shown for the Pair Test compared to standardised measures. Moderate test-retest reproducibility was shown, despite a long time interval between sessions (14 months). Moreover, the Pair Test is able to capture developmental changes in memory, and can therefore chart the developmental trajectory of memory and learning functions across childhood and adolescence. Finally, we used this novel instrument to acquire normative data from 130 typically developing children, aged 8-18 years. Age-stratified normative data are provided for learning, delayed recall and delayed recognition, for measures of verbal and non-verbal memory. The Pair Test thus provides measures of learning and memory accounting for encoding, consolidation and retrieval processes. As such, the standardised test results can be used to determine the status of learning and memory in healthy children, and also to identify deficits in paediatric patients at risk of damage to the neural network underlying mnemonic functions