Is it really better to have your brain lesion early? A revision of the "Kennard principle"

Evolution and ontogeny of neural circuits

Recent studies on neural pathways in a broad spectrum of vertebrates suggest that, in addition to migration and an increase in the number of certain select neurons, a significant aspect of neural evolution is a “parcellation” (segregation-isolation) process that involves the loss of selected connections by the new aggregates. A similar process occurs during ontogenetic development. These findings suggest that in many neuronal systems axons do not invade unknown territories during evolutionary or ontogenetic development but follow in their ancestors' paths to their ancestral targets; if the connection is later lost, it reflects the specialization of the circuitry.

The pattern of interspecific variability suggests (1) that overlap of circuits is a more common feature in primitive (generalized) than in specialized brain organizations and (2) that most projections, such as the retinal, thalamotelencephalic, corticotectal, and tectal efferent ones, were bilateral in the primitive condition. Specialization of these systems in some vertebrate groups has involved the selective loss of connections, resulting in greater isolation of functions. The parcellation process may also play an important role in cell diversification.

The parcellation process as described here is thought to be one of several underlying mechanisms of evolutionary and ontogenetic differentiation.

Factors influencing frontal cortex development and recovery from early frontal injury

BACKGROUND

Neocortical development represents more than a simple unfolding of a genetic blueprint but rather represents a complex dance of genetic and environmental events that interact to adapt the brain to fit a particular environmental context. Although most cortical regions are sensitive to a wide range of experiential factors during development and later in life, the prefrontal cortex appears to be unusually sensitive to perinatal experiences and relatively immune to many adulthood experiences relative to other neocortical regions.

METHODS AND RESULTS

One way to examine experience-dependent prefrontal development is to conduct studies in which experiential perturbations are related neuronal morphology. This review of the research reveals both pre- and post-natal factors have important effects on prefrontal development and behaviour. Such factors include psychoactive drugs, including both illicit drugs and prescription drugs, stress, gonadal hormones and sensory and motor stimulation. A second method of study is to examine both the effects of perinatal prefrontal injury on the development of the remaining cerebral mantle and correlated behaviours as well as the effects of post-injury rehabilitation programmes on the anatomical and behavioural measures.

CONCLUSIONS

Prefrontal injury alters cerebral development in a developmental-stage dependent manner with perinatal injuries having far more deleterious effects than similar injuries later in infancy. The outcome of perinatal injuries can be modified, however, by rehabilitation with many of the factors shown to influence prefrontal development in the otherwise normal brain.

Neural activity-dependent brain changes in development: Implications for psychopathology

In this paper we discuss the contribution of neural activity-dependent factors to shaping the brain in normal and pathologic development, and we discuss factors that determine the likelihood of recovery from the experience of abnormal neural activity during development.

Dynamic self-organization and early lexical development in children

In this study we present a self-organizing connectionist model of early lexical development. We call this model DevLex-II, based on the earlier DevLex model. DevLex-II can simulate a variety of empirical patterns in children's acquisition of words. These include a clear vocabulary spurt, effects of word frequency and length on age of acquisition, and individual differences as a function of phonological short-term memory and associative capacity. Further results from lesioned models indicate developmental plasticity in the network's recovery from damage, in a non-monotonic fashion. We attribute the network's abilities in accounting for lexical development to interactive dynamics in the learning process. In particular, variations displayed by the model in the rate and size of early vocabulary development are modulated by (a) input characteristics, such as word frequency and word length, (b) consolidation of lexical-semantic representation, meaning-form association, and phonological short-term memory, and (c) delayed processes due to interactions among timing, severity, and recoverability of lesion. Together, DevLex and DevLex-II provide an accurate computational account of early lexical development.

Developmental neural plasticity and its cognitive benefits: olivocerebellar reinnervation compensates for spatial function in the cerebellum

The adult mammalian central nervous system displays limited reinnervation and recovery from trauma. However, during development, post-lesion plasticity may generate alternative paths, thus providing models to investigate reinnervation and repair. After unilateral transection of the neonatal rat olivocerebellar path (pedunculotomy), axons from the remaining inferior olive reinnervate the denervated hemicerebellum. Unfortunately, reinnervation to the cerebellar hemisphere is incomplete; therefore, its capacity to mediate hemispheric function (navigation) is unknown. We studied sensorimotor control and spatial cognition of rats with and without transcommissural reinnervation using simple (bridge and ladder) and complex (wire) locomotion tests and the Morris water maze (hidden, probe and cued paradigms). Although pedunculotomized animals completed locomotory tasks more slowly than controls, all groups performed equally in the cued maze, indicating that lesioned animals could orientate to and reach the platform. In animals pedunculotomized on day 3 (Px3), which develop olivocerebellar reinnervation, final spatial knowledge was as good as controls, although they learned more erratically, failing to retain all information from one day to the next. By contrast, animals pedunculotomized on day 11 (Px11), which do not develop reinnervation, did not learn the task, taking less direct routes and more time to reach the platform than controls. In the probe test, control and Px3, but not Px11, animals swam directly to the remembered location. Furthermore, the amount of transcommissural reinnervation to the denervated hemisphere correlated directly with spatial performance. These results show that transcommissural olivocerebellar reinnervation is associated with spatial learning, i.e. even partial circuit repair confers significant functional benefit.

Lesion-Induced Axonal Sprouting in the Central Nervous System

Injury or neuronal death often come about as a result of brain disorders. Inasmuch as the damaged nerve cells are interconnected via projections to other regions of the brain, such lesions lead to axonal loss in distal target areas. The central nervous system responds to deafferentation by means of plastic remodeling processes, in particular by inducing outgrowth of new axon collaterals from surviving neurons (collateral sprouting). These sprouting processes result in a partial reinnervation, new circuitry, and functional changes within the deafferented brain regions. Lesioning of the entorhinal cortex is an established model system for studying the phenomenon of axonal sprouting. Using this model system, it could be shown that the sprouting process respects the pre-existing lamination pattern of the deafferented fascia dentata, i. e., it is layer-specific. A variety of different molecules are involved in regulating this reorganization process (extracellular matrix molecules, cell adhesion molecules, transcription factors, neurotrophic factors, growth-associated proteins). It is proposed here that molecules of the extracellular matrix define the boundaries of the laminae following entorhinal lesioning and in so doing limit the sprouting process to the deafferented zone. To illustrate the role of axonal sprouting in disease processes, special attention is given to its significance for neurodegenerative disorders, particularly Alzheimer's disease (AD), and temporal lobe epilepsy. Finally, we discuss both the beneficial as well as disadvantageous functional implications of axonal sprouting for the injured organism in question.

Behavioral testing and preliminary analysis of the hamster visual system

The dependence of visual orienting ability in hamsters on the axonal projections from retina to midbrain tectum provides experimenters with a good model for assessing the functional regeneration of this central nervous system axonal pathway. For reliable testing of this behavior, male animals at least 10-12 weeks old are prepared by regular pretesting, with all procedures carried out during the less active portion of the daily activity cycle. Using a sunflower seed attached to a small black ball held at the end of a stiff wire, and avoiding whisker contact, turning movements toward visual stimuli are video recorded from above. Because at the eye level, the nasal-most 30 degrees of the visual field can be seen by both the eyes, this part of the field is avoided in assessments of a single side. Daily sessions consist of ten presentations per side. Measures are frequency of responding and detailed turning trajectories. Complete assessment of the functional return of behavior in this testing paradigm takes 3-6 months to complete.

Nano neuro knitting: peptide nanofiber scaffold for brain repair and axon regeneration with functional return of vision

Nanotechnology is often associated with materials fabrication, microelectronics, and microfluidics. Until now, the use of nanotechnology and molecular self assembly in biomedicine to repair injured brain structures has not been explored. To achieve axonal regeneration after injury in the CNS, several formidable barriers must be overcome, such as scar tissue formation after tissue injury, gaps in nervous tissue formed during phagocytosis of dying cells after injury, and the failure of many adult neurons to initiate axonal extension. Using the mammalian visual system as a model, we report that a designed self-assembling peptide nanofiber scaffold creates a permissive environment for axons not only to regenerate through the site of an acute injury but also to knit the brain tissue together. In experiments using a severed optic tract in the hamster, we show that regenerated axons reconnect to target tissues with sufficient density to promote functional return of vision, as evidenced by visually elicited orienting behavior. The peptide nanofiber scaffold not only represents a previously undiscovered nanobiomedical technology for tissue repair and restoration but also raises the possibility of effective treatment of CNS and other tissue or organ trauma.

Compensatory and transneuronal plasticity after early collicular ablation

Plasticity within the visual system was assessed in the quokka wallaby following unilateral superior collicular (SC) ablation at postnatal days (P) 8-10, prior to the arrival of retinal ganglion cell (RGC) axons. At maturity (P100), projections were traced from the eye opposite the ablation, and total RGC numbers were estimated for both eyes. Ablations were partial (28-89% of SC remaining) or complete (0-5% of SC remaining). Projections to the visual centers showed significant bilateral (P < 0.05) increases in absolute volume. Minor anomalous projections also formed within the deep, surviving non-retino-recipient layers of the ablated SC and via a small bundle of RGC axons recrossing the midline to innervate discrete patches in the SC contralateral to the lesion. Total absolute volume of projections did not differ between partial and complete ablations; moreover, values did not differ from normal (P > 0.05). Compared with normal, total RGC numbers were significantly (P < 0.05) reduced in the eye opposite the ablation but increased (P < 0.05) in the other eye. Consequently, the sum of the two RGC populations did not differ from normal (P > 0.05). As in rodents, the visual system in quokka compensates following injury by maintaining a set volume of arborization but does so by forming only minor anomalous projections. Furthermore, increased RGC numbers in the eye ipsilateral to the lesion indicate that compensation occurs transneuronally, thus maintaining total numbers of projecting neurons. The implication is that the visual system acts in concert following unilateral injury to maintain set values for RGC terminal arbors as well as their cell bodies.

Post-lesion transcommissural olivocerebellar reinnervation improves motor function following unilateral pedunculotomy in the neonatal rat

In the adult mammalian central nervous system, reinnervation and recovery from trauma are limited. During development, however, post-lesion plasticity may generate alternate paths providing models to investigate reinnervation and repair. Sometimes, these paths are maladaptive, although the relationship between dysfunction and anatomical abnormality remains unknown. After unilateral transection of the neonatal rat olivocerebellar path (pedunculotomy), axons from the remaining inferior olive reinnervate Purkinje cells in the denervated hemicerebellum with appropriate topography and synaptic function. However, whether this new pathway confers beneficial behavioural effects remains unknown. We studied the behavioural sequelae in rats with and without transcommissural reinnervation using righting and vestibular-drop reflexes, simple locomotion (bridge), complex locomotion (wire) and motor coordination (rotarod) tests. In animals pedunculotomised on day 3 (Px3), which develop olivocerebellar reinnervation, dynamic postural adjustments and complex motor skills develop normally, whereas simple gait is broad-based and slightly delayed. In contrast, Px11 animals, which do not develop reinnervation, have delayed maturation of postural reflexes, gait and complex locomotor skills. In addition, when compared to control animals, their performance in locomotory tasks was slower and the complex task impaired. On the rotarod, control and Px3 animals learned to coordinate their gait and walked for longer at 10 and 20 rpm than Px11 animals. These results show that transcommissural olivocerebellar reinnervation is associated with almost normal motor development and the ability to synchronise gait at slow and moderate speeds, i.e. this reinnervation confers significant behavioural function and is therefore truly compensatory.

Neuroplasticity after unilateral visual cortex damage in the newborn cat

Anatomical, electrophysiological, and behavioral studies implicate extrastriate cortex as a major contributor to the sparing of visually guided behaviors following lesions of primary visual cortex incurred early in life. Here we report considerable sparing of the ability to detect and localize stimuli in the hemifield contralateral to unilateral early lesions of all contiguous visually-responsive primary and extrastriate cortical regions (occipital, visuoparietal, and visuotemporal cortices). In the adult cat this same lesion induces a dense blindness and cats are unable to orient to any visual stimulus introduced into the contralesional hemifield. In the absence of cortical circuits, the neural sparing identified following the neonatal lesion is based on the superior colliculus and it occurs despite massive retrograde transynaptic degeneration of large numbers of retinal ganglion cells.

Stability of vocational outcome in adulthood after moderate to severe preschool brain injury

We studied how moderate to severe childhood traumatic brain injury (TBI) affects vocational outcome with time. This is the second follow-up of patients who were injured as preschoolers in traffic accidents. In the first follow-up the mean age was 23 years and in the present study the average age of the 27-patient cohort was 40 years. Twenty-two patients were assessed clinically by a neuropsychologist, neurologist and a social worker. Five patients, although not able or willing to participate in the clinical study, were contacted by telephone and interviewed on their vocational outcome. Compared to the first follow-up, 20/27 patients in total had no change in their vocational status. Nine out of the 27 patients were working full-time, two had subsidized jobs and 16 were not working. Twenty-four of 27 patients were independent in daily living. In the neuropsychological tests of executive functions, preserved flexibility associated with full-time work status. In conclusion, 1/3 of the patients were still employed full-time over 30 years after the TBI. This suggests that favorable vocational outcome, reached by young adulthood, is maintained at least until middle age.

Animal models of shaken baby syndrome: revisiting the pathophysiology of this devastating injury

To better understand outcomes after early brain injuries, studies must address multiple variables including age at injury, the mechanisms and severity of injury, environmental factors (before and after injury) and developmental factors. Animal models are helpful for elucidating these different aspects. First, this paper describes a new model of shaken baby syndrome (SBS) in mice, without impact or hypoxia. Mortality was 27%; 75% of survivors had focal brain lesions consisting of haemorrhagic or cystic lesions of the white matter, corpus callosum and cerebellum. All shaken animals, with and without focal lesions, showed delayed white matter atrophy. White matter damage and atrophy were reduced by pre-treatment with an NMDA receptor antagonist, indicating that excess glutamate release contributed to the pathophysiology of the lesions. Secondly, it discusses data on neuroprotection after early brain injuries; drugs targeting the NMDA receptors cannot be used in clinical practice but indirect neuroprotection strategies including anti-NO, anti-free radicals and trophic factors hold promise for limiting the excitotoxic white matter damage induced by early injury, in particular caused by shaking, during brain development. Thirdly, it describes two experimental models in which SBS outcomes are determined when the trauma is combined with environmental influences, namely medications during the acute phase, most notably anti-epileptic drugs and rearing conditions.

Greater sparing of visually guided orienting behavior after early unilateral occipital lesions: insights from a comparison with the impact of bilateral lesions

We know that cats with bilateral lesions of occipital visual cortical areas 17, 18 and 19 sustained during the first postnatal week exhibit a modest level of sparing of the ability to re-orient head and eyes to new stimuli relative to cats that incurred equivalent lesions in adulthood. We now report that cats with equivalent unilateral lesions sustained during the first postnatal week (P1-4), or at the end of the first postnatal month (P27-30), orient to stimuli presented in the contralesional field as proficiently as to stimuli introduced into the ipsilesional field. Moreover, levels of proficiency are indistinguishable from those exhibited by intact cats. Thus, the sparing is greater following unilateral lesions than following bilateral lesions, and the level of sparing approaches completeness. The difference between the bilateral and unilateral lesion results suggests types of pathway reorganizations that may emerge as a result of unilateral occipital lesions. We postulate that the greater sparing is based on modifications in both excitatory and inhibitory circuitry linked to the intact hemisphere, and we provide a framework for future investigations that should be relevant to the comprehension of the repercussions of early unilateral and bilateral lesions sustained by monkeys and humans, which also show more robust residual vision following early relative to later damage of occipital cortex.

Developmental disorders of vision

This review of developmental disorders of vision focuses on only a few of the many disorders that disrupt visual development. Given the enormity of the human visual system in the primate brain and complexity of visual development, however, there are likely hundreds or thousands of types of disorders affecting high-level vision. The rapid progress seen in developmental dyslexia and WMS demonstrates the possibilities and difficulties inherent in researching such disorders, and the authors hope that similar progress will be made for congenital prosopagnosia and other disorders in the near future.

Effect of age of onset of temporal lobe epilepsy on the severity and the nature of preoperative memory deficits

The nature and severity of pre-operative memory deficits observed in unilateral temporal lobe epilepsy depend upon a number of variables. Among these variables, age of seizure onset seems to be important. The age at which the lesion is sustained could modify the normal functional organization of the brain. Many studies have examined the effect of age of onset on the severity of memory deficits but have seldom focused on the nature of such deficits (verbal/nonverbal) as a function of epileptic focus laterality. This study investigates the effect of age of onset on the nature and severity of memory impairments. Fifty-six epileptics with unilateral temporal lobe epilepsy and 20 normal subjects were administered a neuropsychological evaluation. Four groups of patients were constituted: left or right temporal lobe epilepsy with early (0-5 years) or late (10 years and over) age of seizure onset. The early group showed major verbal and nonverbal memory deficits. The late group presented minor specific deficits: essentially verbal deficits with left temporal lobe seizures and nonverbal deficits with right temporal lobe seizures. These results may be interpreted in the framework of ontogenesis theories of hemispheric specialization.

Development of the pediatric test of brain injury

OBJECTIVE

The Pediatric Test of Traumatic Brain Injury (PTBI) (currently in its research edition) is a tool for assessing the cognitive-linguistic skills of school-aged children and adolescents in acute care and rehabilitation settings after traumatic brain injury. Development of the PTBI was motivated by the fact that, to date, no standardized test has been available to assess the full range of cognitive-linguistic impairments associated with pediatric brain injury. In this article we describe how the research edition of the PTBI was developed, provide rationale for the areas of assessment, discuss a plan for standardization, and illustrate its use with three children with TBI.

DESIGN

The PTBI was constructed to sample the attention, memory, language, reading, writing, metalinguistic, and metacognitive skills that are particularly at risk in pediatric brain injury and that are relevant to the general education curriculum.

MATERIAL

The test material for the PTBI was selected on the basis of clinical and experimental evidence that children and adolescents with TBI demonstrate a wide range of cognitive and language deficits. These first appear in the early stages of recovery and often persist but change over time.

CONCLUSION

Our goal is to standardize the PTBI so it can be used to establish baseline behaviors and track cognitive-linguistic recovery.

Developmental and lesion effects in brain activation during sentence comprehension and mental rotation

The development of neurocognitive networks was examined in 2 cognitive paradigms: auditory sentence comprehension and mental rotation of alphanumeric stimuli. Patterns of brain activation were measured with whole brain echoplanar functional magnetic resonance imaging at 3 Tesla in 5 adults (20-28 years old), 7 children (9-12 years old), and 6 pediatric patients (9-12 years old) with perinatal strokes or periventricular hemorrhages. Healthy children and adults activated similar neurocognitive networks, but there were developmental differences in the distribution of activity across these networks. In the sentence task, children showed more activation in the inferior visual area suggesting an imagery strategy rather than a linguistic strategy for sentence processing. Furthermore, consistent use of a sentence comprehension strategy, whether correct or incorrect as compared to chance performance, was associated with greater activation in the inferior frontal area (Broca's) in both children and pediatric patients. In the mental rotation task, healthy adults showed more activation in the superior parietal and middle frontal areas and less activation in the supramarginal gyrus, suggesting adults were primarily engaged in visual-spatial manipulation and less engaged in the recognition of noncanonical views of stimuli. The pediatric patients showed patterns of activation consistent with organization of cognitive processing into homologous areas of the contralateral hemisphere.

Psychische und neuropsychologische Folgen von Schädel-Hirn-Traumen im Kindesalter

Zusammenfassung. Die Folgezustände eines schweren Schädel-Hirn-Traumas für das neuropsychologische Leistungsverhalten sind oft sehr weitgehend und beeinträchtigen die spätere soziale Integration der betroffenen Kinder erheblich. Dennoch ergibt sich weder im Verhalten noch im Leistungsbereich ein typisches Syndrommuster, das einem regelhaft auftretenden psychoorganischen Syndrom (POS) entspricht. Aufgrund eigener empirischer Ergebnisse wird deshalb gefordert, die Beurteilung der Auswirkungen eines Schädel-Hirn-Traumas mit spezifischen Untersuchungsmethoden für die psychopathologischen und neuropsychologischen Defizite getrennt voneinander zu erheben. Die sich aus einem solchen differenzierten Vorgehen ableitbaren Befunde besitzen nicht nur akademische Bedeutung, denn erst durch ein entsprechend gründliches Vorgehen lassen sich funktionsspezifische Rehabilitationsmaßnahmen einleiten, die im Interesse der sozialen, schulischen und emotionalen Entwicklung der betroffenen Kinder möglichst früh und gezielt eingesetzt werden sollten.

Cognitive and adaptive outcomes and age at insult effects after non-traumatic coma

Cognitive and adaptive behavioural outcome were studied in the identified survivors of a population based study of non-traumatic coma (NTC) in childhood. Children were assessed early (six weeks) and late (12 months) after NTC. At least 7% of those children in whom no suspicions of prior neurodevelopmental morbidity existed showed moderate or severe disability following NTC. Children over 2 years of age at insult showed some improvement between early and late assessments; however, children below 2 years showed no improvement. Differing age at insult effects were observed between aetiological groups. A relation between early age at first insult and poor outcome was particularly evident among children experiencing NTC caused by epilepsy.

Developmental neuroplasticity in a model of cerebral hemispherectomy and stroke

Cerebral hemispherectomy, a last resort treatment for childhood epilepsy, is a standard procedure which dramatically illustrates the resilience of the brain to extensive damage. If this operation, also mimicking long-term, extensive unilateral capsular stroke, is performed in postnatal cats of up to 60 days of age, there is a remarkable recovery/sparing of neurological functions that is not seen when the lesion occurs during late fetal life or in adulthood. A long-term effect at all ages is loss of neurons in bilateral brain areas remote from the resection site. This is pronounced in adult cats and shows intriguing, paradoxical features in fetal animals, but is substantially attenuated in neonatal cats. Similarly, large-scale reinnervation of subcortical sites (sprouting) by neurons of the remaining, intact hemisphere is prominent in young cats, but not in fetal or adult animals. These and other restorative processes (described herein) in young postnatal animals are matched by relatively higher rates of local cerebral glucose utilization, supporting the notion that they underlie the improved behavioral outcome. Thus, during a critical, defined stage of maturation, presumably common to higher mammals including humans, the brain entirely remodels itself in response to extensive but focal injury. Perhaps the molecular environment allowing for rescue of neurons and enhanced reinnervation at a specific developmental stage could be recreated in subjects with brain lesions at less favorable ages, thereby helping to restore circuitry and spare neurons. However, replacement via transplantation of neurons eliminated by the damage appears to be crucial in attempts to further preserve cells located remotely but yet destined to die or decrease in size. This article presents abundant evidence to show that there is a surprisingly comprehensive long-term morphological remodeling of the entire brain after extensive unilateral damage and that this occurs preferentially during a discrete period of early life. Additional evidence strongly suggests that the remodeling underlies the outstanding behavioral and functional recovery/sparing following early cerebral hemispherectomy. We argue that this period of reduced brain vulnerability to injury also exists in other higher mammals, including man, and suggest ways to enhance restorative processes after stroke/hemispherectomy occurring at other ages.

Memory and socioemotional behavior in monkeys after hippocampal damage incurred in infancy or in adulthood

The present study reviews the long-term effects of neonatal hippocampal damage in monkeys on the development of memory functions and socioemotional behavior. The results showed that neonatal damage to the hippocampal formation impairs specific memory processes, such as those subserving automatic (as opposed to effortful) recognition memory and relational learning, while sparing the abilities to acquire skills, such as object discriminations. Furthermore, the neonatal hippocampectomy led to a progressive loss of social affiliation and a protracted emergence of locomotor stereotypies. While the memory losses following neonatal hippocampal lesions resemble those found after similar lesions acquired in adulthood, only the neonatal lesions resulted in a protracted emergence of abnormal behaviors. These later findings suggested that, presumably, the neonatal lesions impacted on neural systems remote from the site of damage. This was confirmed by our more recent neurobiological studies, demonstrating that neonatal, but not late, lesions of the medial temporal lobe region, disrupt the normal behavioral and cognitive processes subserved by the prefrontal cortex and the caudate nucleus. All together the data support the neurodevelopmental hypothesis viewing early insult to the medial temporal region as the origin of developmental psychosis in humans, such as schizophrenia.

Optimality of the birth population reduces learning and behaviour disorders and sudden infant death after the first month

The weight distribution pattern of all births can be divided into a "skewing to the left" to lower weights and high neonatal mortality, a "skewing to the right" to higher weights (>3500g) and minimum neonatal and postneonatal mortality, and a "symmetrical distribution" with mortality in between. This study was initiated with the hypothesis that a deficit in newborns of more than 3500 g would adversely affect postneonatal death. Higher and rising postneonatal mortality solely attributable to sudden infant death of unknown cause (sudden infant death syndrome; SIDS) was observed in the Nordic countries with a lower proportion of heavy newborns. Minor environmental intervention almost eliminated excess mortality from this cause, supporting raised susceptibility with a depressed birthweight in postneonatal SIDS. This contrasts with classical neonatal low birthweight SIDS, which is stable despite numerous attempts at reduction, supporting a multi-factorial aetiology: low maternal age, low education, low socioeconomic status, maternal smoking, infection, etc. The postneonatal SIDS epidemic associated with a deficit in heavy newborns is thought to be a result of changing behaviour in pregnancy: moderate iatrogenic dietary restriction and young women favouring a low-calorie, low-fat diet, especially in the third trimester when the foetus is most vulnerable, which delays myelination and somatic growth and renders the infant susceptible to minor morbidity and irregularity. The timing of death and neuropathological findings suggestive of repeated hypoxic episodes in more than 80% of cases of SIDS prior to death support this theory. The similar weight distribution patterns in SIDS and all births in Denmark, the UK and the USA suggest a substantial proportion of the neonates in these countries could be growth-retarded and at risk of hypoxic episodes in infancy. A few cases, particularly males (sex-ratio = 1.7), suffer SIDS, the majority survive. Many, mostly males, present minor CNS signs and learning and behaviour problems. The male predominance accords with males more than 500 g higher optimal birthweight than females and susceptibility to a depressed weight at birth. In order to prevent postneonatal dying, SIDS and reduce learning/behaviour disorders it is necessary to raise the proportion of heavy newborns by promoting foetal growth rate equal to the maternal intrinsic rate by eating to one's appetite a balanced diet, favouring a diet high in marine fat, especially in third trimester, in order to ensure maturation of the CNS and prolong gestation, thereby increasing birthweight. Although the increased survival of some very low birthweight neonates confounds the issue, a division between SIDS in neonatal and postneonatal death is recommended in order to assess the proportion of "avoidable infant death" as opposed to persistent classical neonatal SIDS.

Language organization in patients with early and late left-hemisphere lesion: a PET study

Functional neuroimaging studies have shown enhanced right-hemisphere language activations in adults with left-hemisphere damage. We hypothesized that this effect would be stronger in patients with lesion occurring early in development. Using [15O]-water PET, we studied eight normal adults and 23 patients with unilateral left lesion during rest, listening to sentences, and sentence repetition. Thirteen patients had lesions with early onset (< 5 years) and ten had lesions with late onset (> 20 years). For listening to sentences, frontotemporal blood flow increases were significantly stronger in the left than in the right hemisphere in normal adults. This normal asymmetry was reduced in patients with late lesion and reversed in those with early lesion. For sentence repetition, analogous group differences were significant for the basal ganglia, but failed to reach significance for the (pre)motor and insular regions. We conclude that left lesion leads to alterations in the asymmetry of language activations (in and beyond the perisylvian areas). In addition, rightward shifts of language activation tend to be stronger as a consequence of early (as compared to late) lesion. Finally, postlesional reorganization appears to reflect a coexistence of 'additive' and 'subtractive' effects, i.e., activation in some regions that are not normally involved in language processing and lack of activation in other (undamaged) regions that are normally activated by language tasks.

Brain organization for language in children, adolescents, and adults with left hemisphere lesion: a PET study

1. There is evidence for pronounced brain plasticity during postnatal maturation. The authors hypothesized that left-hemisphere lesion would be associated with greater than normal language participation of the right hemisphere and that atypical asymmetry of perisylvian language activations would be enhanced after lesion occurring in early childhood as compared to lesion occurring later in life. 2. Eleven patients with left-hemisphere lesion (aged 8-33 yrs.) and 9 normal adult comparison subjects were studied, using [15O]-water positron emission tomography. One patient group (N = 6) had early lesion onset (< or = 6 years of age), a second group (N = 5) had lesion onset later in life (> or = 10 years of age). Regional cerebral blood flow (rCBF) changes during listening to sentences (minus rest) and sentence generation (minus repetition) were compared between groups in predefined regions of interest. 3. Variance of regional activations within early and late lesion onset groups was considerable and qualitative inspection revealed only few robust group differences. However, when 4 patient pairs were approximately matched for chronological age, lesion site and VIQ, significantly reduced leftward asymmetry of activations in early lesion patients was found in the prefrontal, inferior frontal, and inferior parietal regions for expressive language, with concordant and marginally significant trends in the inferior frontal and superior temporal regions for receptive language. 4. The results suggest enhanced postlesional plasticity in childhood, while also reflecting strong individual variability probably due to clinical and demographic factors beside lesion onset.