Lesion size and recovery of function: some new perspectives

Plasticity in the developing brain: neurophysiological basis for lesion-induced motor reorganization

The plasticity of the developing brain can be observed following injury to the motor cortex and/or corticospinal tracts, the most commonly injured brain area in the pre- or peri-natal period. Factors such as the timing of injury, lesion size and lesion location may affect a single hemisphere’s ability to acquire bilateral motor representation. Bilateral motor representation of single hemisphere origin is most likely to occur if brain injury occurs before the age of 2 years; however, the link between injury aetiology, reorganization type and functional outcome is largely understudied. We performed a retrospective review to examine reorganized cortical motor maps identified through transcranial magnetic stimulation in a cohort of 52 patients. Subsequent clinical, anthropometric and demographic information was recorded for each patient. Each patient’s primary hand motor cortex centre of gravity, along with the Euclidian distance between reorganized and normally located motor cortices, was also calculated. The patients were classified into broad groups including reorganization type (inter- and intrahemispheric motor reorganization), age at the time of injury (before 2 years and after 2 years) and injury aetiology (developmental disorders and acquired injuries). All measures were analysed to find commonalities between motor reorganization type and injury aetiology, function and centre of gravity distance. There was a significant effect of injury aetiology on type of motor reorganization (P < 0.01), with 60.7% of patients with acquired injuries and 15.8% of patients with developmental disorders demonstrating interhemispheric motor reorganization. Within the interhemispheric motor reorganization group, ipsilaterally and contralaterally projecting hand motor cortex centres of gravity overlapped, indicating shared cortical motor representation. Furthermore, the data suggest significantly higher prevalence of bilateral motor representation from a single hemisphere in cases of acquired injuries compared to those of developmental origin. Functional outcome was found to be negatively affected by acquired injuries and interhemispheric motor reorganization relative to their respective counterparts with developmental lesions and intrahemispheric motor reorganization. These results provide novel information regarding motor reorganization in the developing brain via an unprecedented cohort sample size and transcranial magnetic stimulation. Transcranial magnetic stimulation is uniquely suited for use in understanding the principles of motor reorganization, thereby aiding in the development of more efficacious therapeutic techniques to improve functional recovery following motor cortex injury.

Simulating lesion-dependent functional recovery mechanisms

Functional recovery after brain damage varies widely and depends on many factors, including lesion site and extent. When a neuronal system is damaged, recovery may occur by engaging residual (e.g., perilesional) components. When damage is extensive, recovery depends on the availability of other intact neural structures that can reproduce the same functional output (i.e., degeneracy). A system's response to damage may occur rapidly, require learning or both. Here, we simulate functional recovery from four different types of lesions, using a generative model of word repetition that comprised a default premorbid system and a less used alternative system. The synthetic lesions (i) completely disengaged the premorbid system, leaving the alternative system intact, (ii) partially damaged both premorbid and alternative systems, and (iii) limited the experience-dependent plasticity of both. The results, across 1000 trials, demonstrate that (i) a complete disconnection of the premorbid system naturally invoked the engagement of the other, (ii) incomplete damage to both systems had a much more devastating long-term effect on model performance and (iii) the effect of reducing learning capacity within each system. These findings contribute to formal frameworks for interpreting the effect of different types of lesions.

A New Insight on the Role of the Cerebellum for Executive Functions and Emotion Processing in Adults

Objective: We investigated whether the cerebellum plays a critical or supportive role in in executive and emotion processes in adults. Many investigators now espouse the hypothesis that participants with cerebellar lesions experience executive functions and emotions (EE) disorders. But we hypothesized that these disorders would be milder if the damage is relatively limited to the cerebellum compared to damage involving the cerebellum plus additional cortical areas. Methods: We studied veterans with penetrating Traumatic Brain Injury (pTBI) participating in the Vietnam Head Injury Study (VHIS). We selected veterans with a cerebellar lesion (n = 24), a prefrontal cortex lesion (n = 20), along with healthy controls (HC) (n = 55). Tests of executive functions and emotions were analyzed as well as caregiver burden. We performed between-group null hypothesis significance testing, Bayesian hypothesis tests and correlational analyses. Results: Performance of participants with cerebellar lesions which extended to the cerebral cortex was similar to the HC on the Executive Function tests but they were significantly impaired on the Working Memory Index. No differences were found on the emotional processing tasks with one exception-the Facial Expression of Emotion-Test (FEEST). We then examined a sub-group of participants with large cerebellar lesions (>15%) but minimal lesions in the cerebral cortex (<15%). This sub-group of participants performed similarly to the HC on the Working Memory Index and on the FEEST. Conclusions: We suggest that the cerebellar cortex may not be critical for executive functions or processing emotional stimuli in adults as suggested. Instead, we find that the cerebellum has a supportive role characterized by its computing of the motor requirements when EE processing is required.

Machiavellian tendencies increase following damage to the left dorsolateral prefrontal cortex

Machiavellianism - a personality trait that is characterized by a tendency to distrust, deceive and exploit others - has been the focus of growing attention in psychological research. Neuroimaging studies of Machiavellianism highlight the influence of the dorsolateral prefrontal cortex (dlPFC) on Machiavellianism tendencies. However, knowledge regarding the causal role of the left and right dlPFC on Machiavellianism is still obscure. Here, we measured general Machiavellian tendencies, as well as two subscales (i.e., Machiavellian Views and Machiavellian Tactics) in a large sample of brain-injured patients (N = 129) and non-brain-injured control participants (N = 37) to determine whether Machiavellianism tendencies can be altered by brain damage. We analyzed Machiavellianism tendencies as a function of lesion location, with patients separated into four groups based on dlPFC damage: left dlPFC damage, right dlPFC damage, non-dlPFC damage, and healthy controls. We found that left dlPFC damage increased Machiavellianism in general, and Machiavellian perspective (views) in particular, but did not modulate behavior (tactics). Critically, left dlPFC damage predicted higher levels of Machiavellianism after controlling for general and emotional intelligence, linguistic abilities, empathy and psychopathology. These findings establish a causal role of the left dlPFC in modulating Machiavellian views, and indicate that one can hold Machiavellian views without necessarily endorsing Machiavellian tactics.

The outcome of a second stroke: the impact on hemispheric functioning

A total of 238 patients admitted to Loewenstein Rehabilitation Hospital (LRH) after a second stroke were included in a preliminary study on the outcome of rehabilitation. The patients were examined for activities of daily living (ADL), locomotion, hand function, elementary cognitive abilities, and communication. The practical goal was to examine the rehabilitation prognosis of patients who suffered brain stroke for a second time. On the theoretical plane, the study aimed to broaden knowledge of the functional relationships between the two cerebral hemispheres from a rehabilitation perspective. A major finding is that recovery from a recurrent stroke is a multifactorial affair. Communication and spatial abilities are directly related to hemispheric specialization, whereas locomotion and hand functioning are rather organismic functions.

Acquired alexithymia following damage to the anterior insula

Alexithymia is a subclinical condition characterized by impaired awareness of one's emotional states, which has profound effects on mental health and social interaction. Despite the clinical significance of this condition, the neurocognitive impairment(s) that lead to alexithymia remain unclear. Recent theoretical models suggest that impaired anterior insula (AI) functioning might be involved in alexithymia, but conclusive evidence for this hypothesis is lacking. We measured alexithymia levels in a large sample of brain-injured patients (N=129) and non-brain-injured control participants (N=33), to determine whether alexithymia can be acquired after pronounced damage to the AI. Alexithymia levels were first analysed as a function of group, with patients separated into four groups based on AI damage: patients with >15% damage to AI, patients with <15% damage to AI, patients with no damage to AI, and healthy controls. An ANOVA revealed that alexithymia levels varied across groups (p=0.009), with >15% AI damage causing higher alexithymia relative to all other groups (all p<0.01). Next, a multiple linear regression model was fit with the degree of damage to AI, the degree of damage to a related region (the anterior cingulate cortex, ACC), and the degree of damage to the whole brain as predictor variables, and alexithymia as the dependent variable. Critically, increased AI damage predicted increased alexithymia after controlling for the other two regressors (ACC damage; total lesion volume). Collectively, our results suggest that pronounced AI damage causes increased levels of alexithymia, providing critical evidence that this region supports emotional awareness.

Cognitive assessment in epilepsy surgery of children

INTRODUCTION

Although the neurocognitive assessment in children as in the adults is an important step before and after surgery, in the literature, the data about pre- and postoperative neurocognitive evaluations in children are very few.

OBJECTIVE

The purpose of this paper is to consider some peculiar aspects of the neurocognitive assessment during development, and report literature data about neuropsychological outcome of epileptic children treated with focal resection and hemispherectomy.

RESULTS AND DISCUSSION

The second section concerns our personal experience about a cohort of 45 children with refractory epilepsy operated on before 7 years. The results suggest that early surgical treatment is generally effective for seizure control and behavior improvement in children with refractory epilepsy. Concerning cognitive outcome, we found that the neurocognitive level was unchanged in the majority of the patients.

CONCLUSION

We underline the importance of multicentric studies with standardized neuropsychological assessments in large series of young children.

Developmental plasticity after right hemispherectomy in an epileptic adolescent with early brain injury

OBJECTIVES

The authors present the case of an adolescent affected with refractory epilepsy due to a neonatal ischemic infarction of the right medial cerebral artery. Hemiplegic since the first months of life, she began presenting motor partial seizures associated with drop attacks at 4.5 years; these were initially well controlled by antiepileptic drugs, but at 10 years seizures appeared again and became refractory. Thus, at 14 years and 10 months, she was submitted to a right hemispherectomy that made her rapidly seizure free. In the post-surgical follow-up lasting 5 years, neuropsychological serial assessments showed an impressive progressive improvement of cognitive skills, namely, visuospatial abilities. This case seems to challenge the widely spread feeling that functional catch-up in brain-injured children could only occur early in life. In effect, the astonishing recovery especially of visuospatial skills in our case occurred in adolescence after a late surgical intervention of right hemispherectomy.

METHODS

Different neuropsychological aspects are discussed. The reorganisation process recovered the spatial and linguistic abilities as well as the verbal and visuospatial memory; however, there was a persistent impairment of complex spatial and perceptual skills as well as recall abilities. Despite the deficit of complex visual stimuli processing, the patient showed a good performance in the recognition of unknown faces.

CONCLUSIONS

Probably, the absence of seizures in the first 4 years of life could have allowed a generally adequate compensatory reorganisation, successively masked by the persistent and diffuse epileptic disorder. The seizure control produced by surgery eventually made evident the effectiveness of the brain reorganisation.

Anoxic Versus Traumatic Brain Injury: Amount of Tissue Loss, Not Etiology, Alters Cognitive and Emotional Function

Research in neuropsychology suggests that the etiology of a neurologic injury determines the neuropathological and neuropsychological changes. This study compared neuropsychological outcome in subjects who had traumatic brain injury (TBI) with subjects who had anoxic brain injury (ABI), who were matched for age, gender, and ventricle-to-brain ratio. There were no group differences for morphologic or neuropsychological measures. Both groups exhibited impaired memory, attention, and executive function, as well as slowed mental processing speed. Intelligence correlated with whole brain volume, and measures of memory correlated with hippocampal atrophy. There was no unique contribution of hippocampal atrophy on neuropsychological outcome between the groups. In the absence of localized lesions, the amount of neural tissue loss, rather than etiology, may be the critical factor in neuropsychological outcome.

Tetrodotoxin infusions into the dorsal hippocampus block non-locomotor place recognition

The hippocampus is critical for navigation in an open field. One component of this navigation requires the subject to recognize the target place using distal cues. The experiments presented in this report tested whether blocking hippocampal function would impair open field place recognition. Hungry rats were trained to press a lever on a feeder for food. In Experiment 1, they were passively transported with the feeder along a circular trajectory. Lever pressing was reinforced only if the feeder was passing through a 60 degrees -wide sector. Thus, rats preferentially lever pressed in the vicinity of the reward sector indicating that they recognized its location. Tetrodotoxin (TTX) infusions aimed at the dorsal hippocampi caused rats to substantially increase lever pressing with no preference for any region. The aim of Experiment 2 was to determine whether the TTX injections caused a loss of place recognition or a general increase of lever pressing. A separate group of rats was conditioned in a stationary apparatus to press the lever in response to a light. The TTX injections did not abolish preferential lever pressing in response to light. Lever pressing increased less than half as much as the TTX-induced increase in Experiment 1. When these animals with functional hippocampi could not determine the rewarded period because the light was always off, lever pressing increased much more and was similar to the TTX-induced increase in Experiment 1. We conclude that the TTX inactivation of the hippocampi impaired the ability to recognize the reward place.

Recovery of movement-related potentials in the temporal course after prefrontal traumatic brain injury: a follow-up study

OBJECTIVE

The movement-related potential (MRP) is an EEG measure related to self-initiated movements, consisting of the Bereitschaftspotential (BP), the negative slope, and the motor potential. Since in a former study the BP was reduced in acute prefrontal traumatic brain injury (TBI) patients, the present study examined the MRPs' course in follow-up examinations.

METHODS

Right index finger MRPs of 22 patients with contusions of the prefrontal cortex were recorded 12, 26, and 52 weeks after TBI and compared to controls.

RESULTS

Within the patient group, a significant increase of the BP in the temporal course after TBI was observed. MRPs 12 and 26 weeks after TBI did not differ significantly from the control group. One year after TBI, significantly enhanced BPs were found.

CONCLUSIONS

In the temporal course after prefrontal TBI, a recovery of the initially reduced BP was observed. The enhanced BP areas 1 year after TBI might represent the need for increased cognitive resources during movement preparation, supporting a recovered, but less effective neuronal network.

SIGNIFICANCE

The present study represents the first longitudinal follow-up study of MRPs after prefrontal brain lesion. The observed changes reflect the plastic capacity of the brain, reorganizing the neuronal network function.

Factors contributing to motor impairment and recovery after stroke

The goal of the present study was to examine factors affecting motor impairment and recovery in a primate model of cortical infarction. Microelectrode stimulation techniques were used to delineate the hand representation in the primary motor cortex (M1). Microinfarcts affecting approximately 30% of the hand representation were made by electrocoagulation of surface vessels. Electrophysiologic procedures were repeated at 1 month after the infarct to examine changes in motor map topography. Before the infarct, and at approximately 1 week (early period) and 1 month (late period) after the infarct, manual performance was assessed on a reach-and-retrieval task that required skilled use of the digits. Contrary to the expected outcome, early impairment was inversely related to the amount of digit representation destroyed by the infarct. That is, animals with less involvement of the M1 digit area demonstrated the greatest motor deficit in the early postinfarct period. In addition, improvement in motor performance between early and late postinfarct periods was directly related to a decrease in the extent of the digit + wrist/forearm area in the final postinfarct map. These results suggest that specific aspects of motor-map remodeling are expressions of adaptive mechanisms that underlie functional recovery after stroke. Further, they suggest that the adaptive mechanisms underlying postinjury recovery differ in detail from those that operate in normal motor learning. The potential role of compensatory mechanisms in these phenomena is discussed.

Comparing the Fused Dichotic Words Test and the Intracarotid Amobarbital Procedure in children with epilepsy

The validity of the Fused Dichotic Words Test (FDWT) in predicting the nature of speech representation, as determined by the Intracarotid Amobarbital Procedure (IAP), was examined in a sample of 28 children with epilepsy. Various methods of analysis (difference score, lambda, and lambda(*)), for the FDWT data were calculated and compared. Results showed the validity of the FDWT did not change depending on the method of analysis. The difference scores showed that 18 of the 19 patients with left hemisphere speech obtained right-ear advantages, while the patient with right hemisphere speech showed a left-ear advantage. As a group, patients with left-hemisphere speech obtained a statistically significant right-ear advantage for the lambda and lambda(*) indices, while the patient with right-hemisphere speech showed a left-ear advantage that was also significant for both lambda measures. Patients with bilateral speech, as a group, displayed a non-significant ear advantage. Some of the scores from the left-hemisphere group overlapped with those from patients with bilateral speech representation. Controlling for stimulus dominance effects using the lambda(*) measure did not improve classification accuracy for nature of speech representation based on FDWT scores. Finally, comparison of our data using the laterality index from a similar study, showed scores smaller in magnitude than that found in adults with epilepsy.

Loss of the innate cortical engram for action patterns used in skilled reaching and the development of behavioral compensation following motor cortex lesions in the rat

Damage to the motor cortex of the rat (Rattus norvegicus) impairs skilled movements used in reaching for food with the contralateral forepaw. Nevertheless, there is substantial recovery in success over a two-week postsurgical period. The profile of behavioral recovery is believed to reflect the eventual normalization of behavior, but this idea has not been explicitly examined. The present experiments examined postsurgical reaching success and reaching movements as a function of (1) lesion type, (2) lesion size, (3) lesion location, (4) depletion of forebrain noradrenaline, and (4) presurgical and postsurgical experience. The results show that at least two separate processes contribute to recovery in postsurgical performance. The early postsurgical period was characterized by extreme difficulties in making reaching movements. The experiments suggest that this initial impairment was due to the loss of the innate cortical engram that supports the action patterns used for skilled movements. Subsequent recovery in reaching success was not due to the reacquisition of normal movements, but was due rather to the use of compensatory movements. The results are discussed in relation to the idea that true recovery from motor cortex injury will require that damaged neurons and their connections be rescued or replaced.

Paradoxical facilitation of a free recall of nonwords in persons with traumatic brain injury

Brain damage is usually associated with behavioral deficits. However, there is an increasing amount of evidence that lesions of some brain regions are associated with improvements instead of impairments of certain behaviors. We report the results of a study of free recall performance in subjects with traumatic brain injury. One-fourth of the subjects displayed above-normal performance in recall of nonwords. No such facilitation was found with nine lists of words.

Neurocognitive sequelae of scaphocephaly

OBJECTIVE

Early cranioplasty for scaphocephaly has become routine in most countries. In addition to normalizing the shape of the skull, it has been found to decrease intracranial hypertension. Whether corrective surgery benefits the child's cognitive outcome has been poorly documented.

DESIGN

Eighteen children whose sagittal suture showed premature fusion at birth or soon thereafter were operated on at age 1 week to 7 months. All patients healed without complications and were followed-up at regular intervals. At the age of 7.8 to 16.3 years they were examined to clarify their neurocognitive development and to compare the results with their age- and gender-matched healthy controls.

RESULTS

Originally scaphocephalic children, although operated on, had mild deficiencies in auditory short-term memory and language development when examined with the general comprehension, similarities, and digit span subscales of the Wechsler Intelligence Scale for Children-Revised. In all other respects their developmental outcome was equal to that of the controls.

CONCLUSIONS

Despite relative early correction of the skull shape, originally scaphocephalic children's neurocognitive performances do not reach the same level in all of the neurocognitive domains as their matched controls at school age. Early operation (</=1 month) may decrease this developmental delay. This implies that impairment of brain function has already taken place in utero. For the same reason an early operation seems to be justified not only for correction of the skull shape, but also to allow unrestricted development for the brain. Postponement of the operation would not serve either of these aims.

Medial forebrain bundle lesions fail to structurally and functionally disconnect the ventral tegmental area from many ipsilateral forebrain nuclei: implications for the neural substrate of brain stimulation reward

Lesions in the medial forebrain bundle rostral to a stimulating electrode have variable effects on the rewarding efficacy of self-stimulation. We attempted to account for this variability by measuring the anatomical and functional effects of electrolytic lesions at the level of the lateral hypothalamus (LH) and by correlating these effects to postlesion changes in threshold pulse frequency (pps) for self-stimulation in the ventral tegmental area (VTA). We implanted True Blue in the VTA and compared cell labeling patterns in forebrain regions of intact and lesioned animals. We also compared stimulation-induced regional [14C]deoxyglucose (DG) accumulation patterns in the forebrains of intact and lesioned animals. As expected, postlesion threshold shifts varied: threshold pps remained the same or decreased in eight animals, increased by small but significant amounts in three rats, and increased substantially in six subjects. Unexpectedly, LH lesions did not anatomically or functionally disconnect all forebrain nuclei from the VTA. Most septal and preoptic regions contained equivalent levels of True Blue label in intact and lesioned animals. In both intact and lesioned groups, VTA stimulation increased metabolic activity in the fundus of the striatum (FS), the nucleus of the diagonal band, and the medial preoptic area. On the other hand, True Blue labeling demonstrated anatomical disconnection of the accumbens, FS, substantia innominata/magnocellular preoptic nucleus (SI/MA), and bed nucleus of the stria terminalis. [14C]DG autoradiography indicated functional disconnection of the lateral preoptic area and SI/MA. Correlations between patterns of True Blue labeling or [14C]deoxyglucose accumulation and postlesion shifts in threshold pulse frequency were weak and generally negative. These direct measures of connectivity concord with the behavioral measures in suggesting a diffuse net-like connection between forebrain nuclei and the VTA.

Positive and negative factors in movement control: a current review of Denny-Brown's hypothesis

In his extensive writings, Denny-Brown hypothesized that two competitive 'tropisms,' one positive (exploratory) and one negative (withdrawal) act to coordinate normal movements at all levels of the neuraxis. Lesions in particular areas of the central nervous system result in disequilibrium between these tropisms, leading to disorders of posture and movement, including involuntary movements. The tactile manifestations of unbalanced exploratory tropisms are grasping responses, whereas the complementary withdrawal tropisms are avoiding responses. In Denny-Brown's view, at the level of the cerebral cortex, grasping responses result from frontal lobe injury whereas avoiding responses result from parietal lobe lesions. In this report we review Denny-Brown's conceptions of positive and negative tropisms, their anatomical loci, and whether his hypothesis has merit in a contemporary approach to brain function. We find that Denny-Brown's view on the anatomical loci associated with these behaviors is incomplete, but that the idea of conflicting behavioral tendencies is valuable for understanding and managing some neurological and perhaps also psychiatric disorders. For example, his hypothesis offers an important perspective in understanding the paradoxical success of stereotaxic surgery to alleviate the symptoms of Parkinson's disease.

A theory of neurolinguistic development

This article offers a developmental theory of language and the neural systems that lead to and subserve linguistic capabilities. Early perceptual experience and discontinuities in linguistic development suggest that language develops in four phases that occur in a fixed, interdependent sequence. In each phase of language, a unique ontogenetic function is accomplished. These functions have proprietary neural systems that vary in their degree of specialization. Of particular interest is an analytical mechanism that is responsible for linguistic grammar. This mechanism is time-locked and can only be turned on in the third phase. Confirming evidence is provided by children who are delayed in the second phase of the language learning process. These children store insufficient lexical material to activate their analytic mechanism. Inactivation behaves like damage, shifting language functions to homologous mechanisms in the nondominant hemisphere, thereby increasing functional and anatomical symmetry across the hemispheres. This atypical assembly of neurolinguistic resources produces functional but imperfect command of spoken language and may complicate learning of written language. The theory thus offers a different role for genetics and early experience, and a different interpretation of neuroanatomic findings, from those entertained in most other proposals on developmental language disorders.

Memory beyond the hippocampus

Improved neuroanatomical knowledge, technical and methodological innovations (such as PET), and more refined conceptualizations of memory have inspired a reappraisal of theoretical beliefs regarding the role of the hippocampus in memory. In the past few years, it has become apparent that the influence of the medial temporal lobe regions extends beyond memory and that memory processes (such as encoding, consolidation and retrieval) involve not only the hippocampus and the medial temporal and diencephalic regions, but also widely distributed neocortical and perhaps even cerebellar regions.

Radiosurgery for cerebral AVMs in children and adolescents: the neurobehavioral outcome

Eight patients, ranging in age from 9 to 18 years, were treated for arteriovenous malformations using gamma knife radiosurgery and were evaluated an average of 6 years after treatment to record potential effects of radiosurgery on cognitive and neuropsychological performance. Tests for general intelligence, nonverbal intelligence, memory and its components, and attention performance were administered to patients and compared with test results of age-matched siblings or first cousins. No statistically significant difference was found between the performance of patients and controls in any of the tests administered. Additionally, a specially designed questionnaire completed by the patients, their parents, and their teachers revealed that the patients' emotional and relational behavior was stable and unchanged after treatment. No correlation was found between the neurocognitive test performance and the lesion volumes irradiated, but the lesion site was found to contribute to the type of deficit recorded after treatment. The less invasive nature of the radiosurgical approach, combined with the brevity or absence of hospitalization, presumably contributed to the patients successful physical, mental, and emotional recovery.

Functional brain reorganization in children

Developmental brain plasticity in association with focal brain injury is dependent on a number of factors, including age of the individual at the time of injury, size and topography of the brain lesion, maturational state of the brain system injured, integrity of brain areas surrounding and contralateral to the lesion, presence and duration of epilepsy, and medication effects. Recently developed functional neuroimaging tools now make it possible to study non-invasively several aspects of human brain functional reorganization in response to injury. Clinical models which are suitable for the study of developmental brain plasticity include patients who have undergone cortical resections for the alleviation of intractable epilepsy, patients who have sustained unilateral cerebrovascular insults at various periods of development, patients with chronic progressive unilateral brain injury such as in the Sturge-Weber syndrome, and patients with early sensory deprivation such as blind or deaf subjects. Although evidence of functional brain reorganization can be demonstrated in these models, it is emphasized that the neurobiological rules that govern intrahemispheric versus interhemispheric reorganization of function in the brain are, at present, poorly understood.

Motor function of infants with spastic hemiplegia

The motor function of 25 children with spastic hemiplegia was examined retrospectively using videotapes recorded at 2-8 months of age. Many infants showed deficient forward movement of the arm and deficient opening of the hand on the affected side. At 7 and 8 months of age, whether the hand was semiflexed or clenched was correlated with the later upper extremity function. In the prone position, most could support their weight on the flexed arm on the affected side. In the supine position, half of the infants could not extend the knee on the affected side. At 2 months of age, asymmetry of the upper and lower extremity movements was not identified. Persistent primitive reflexes and abnormal truncal muscular tone were not recognized in the hemiplegic infants, and did not seem to be signs predicting hemiplegic cerebral palsy.

Metabolic recovery in caudate nucleus of children following cerebral hemispherectomy

In 3 children who had undergone cerebral hemispherectomy (hemidecortication) between the ages of 1 year 5 months and 4 years for the alleviation of intractable epilepsy, cerebral glucose utilization was studied serially with positron emission tomography. Three to 7 months after hemispherectomy, glucose utilization in the caudate nuclei on the side of hemispherectomy had decreased to below preoperative values, presumably due to total deprivation of ipsilateral cortical input. One to 2.5 years after surgery, complete restoration of glucose metabolic activity to preoperative levels was seen in 2 patients and partial recovery was seen in 1 patient. These alterations of cerebral glucose utilization are believed to reflect microscopic anatomical reorganizational changes (e.g., collateral sprouting) that have been documented following similar lesions in several animal models. Our findings suggest that positron emission tomography may provide a sensitive measure of developmental brain plasticity in vivo.

Domains of rehabilitation: a theoretical perspective

On the basis of a taxonomy of functions an outline is given on potential deficits after brain lesions. The taxonomy distinguishes between "what"- and "how"-functions. Whereas for what-functions the localizing principle may apply, the how-functions being responsible for the logistics of the brain are non-locally represented. After brain injury the what- and how-functions may be differentially effected. On this basis 4 domains of functional rehabilitation can be distinguished, namely restitution and substitution of function after partly or complete losses of what-functions, activation and integration of function after alterations of activation or a disruption of functional coordination. Different strategies of functional rehabilitation are related to basic neurobiological principles which have been made responsible for restitution of function. Neuropsychological rehabilitation remains a challenge for neurobiology.

Pathological left-handedness and preserved function associated with a slowly evolving brain tumor

The authors report the serial neuropsychological evaluations of a patient with acquired left-handedness who had a massive brain tumor that infiltrated the entire temporal and posterior parietal lobes of the left hemisphere. Although the patient had pre-operative impairment of non-verbal memory, follow-up assessment 31 and 66 months after the tumor was resected revealed cognitive functions to be in the high-average to superior range. This case demonstrates the sparing of neuropsychological functions that can be seen with a slowly evolving lesion. The authors suggest that such functional sparing may be due to transfer of function rather than to the residual function of tumor-infiltrated neuronal tissue. Possible mediators of functional preservation include slow lesion growth, the patient's youth at disease onset and the large size of the lesion.

Memory disturbances following anterior communicating artery rupture

Thirty patients with lesions due to the rupture and repair of an aneurysm of the anterior communicating artery were compared neuropsychologically with 27 patients with ruptures but no lesions and 30 normal control subjects. Patients with combined lesions in the basal forebrain and striatum (n = 5), or basal forebrain, striatum, and ventral frontal cortex (n = 7), had severe memory deficits, whereas patients with lesions in the basal forebrain (n = 7) or the striatum (n = 5) alone showed virtually no deficits. Patients with lesions of the basal forebrain and ventral frontal cortex together (n = 6) showed mild memory deficits. In contrast to the memory effects, emotional changes were most pronounced in patients with striate lesions alone. Basal forebrain or ventral frontal lesions ameliorated rather than aggravated the emotional effects of striate lesions. It is suggested that the basal forebrain and the striatum form links of different pathways related to mnemonic information processing. Both systems may be able to compensate for a dysfunction of the other, but lesions of both systems together may lead to strong and unrecoverable memory deficits.

Neonatal cerebral infarction: symptoms, CT findings and prognosis

In a retrospective multi-center study, we investigated eighteen infants with unilateral cerebral infarctions confirmed by computed tomography (CT) scans. The initial symptoms were observed in all the patients between 0 and 3 days of age. Convulsions or apneic attacks were the initial symptoms in all but one. Only 4 patients had complicated obstetric histories and none showed polycythemia or electrolyte abnormalities. All of the initial CT scans revealed unilaterally localized hypodense areas. In 10, the initial CT scans were performed within 24 hours after the clinical onset. In 16, the lesions were within the territory of the middle cerebral artery, 9 of which also involved the cortico-spinal tract (CST). In the remaining 2 patients, the lesions were located within the territory of the posterior cerebral artery. None of the 9 patients without CST involvement developed hemiplegia, whereas 5 (56%) of the 9 with CST involvement had hemiplegia, which is a fairly low incidence compared with that in adult cases. This difference was thought to be related to neonatal brain plasticity.

Assessment of upper and lower extremity movements in hemiplegic children

Upper and lower extremity movements were assessed in 26 children with spastic hemiplegia according to the modified Brunnstrom method. Of the upper extremity movements, supinating the forearm was most difficult, followed in order by pronating the forearm, flexing the shoulder to 90 degrees, flexing the shoulder to 180 degrees, abducting the shoulder to 90 degrees or putting the hand on the lumbar spine, putting the hand behind the ipsilateral ear (flexor synergy), and putting the hand on the contralateral knee (extensor synergy). The extensor and flexor synergies were easier than the other movements in the hemiplegic children as well as in hemiplegic adults, but the order of difficulty in the other movements in children was not the same as in adults. The difficulty in the lower extremity movements was uniform in the subjects. None of the children could dorsi-flex the ankles and many could not rotate the hips internally. A small number of the children could not flex the knees or perform straight leg raising. All children could flex the hips and knees, extend the hips and knees, and abduct the hips. The difficulty in isolated hip abduction and flexion was less prominent in the hemiplegic children, compared to in hemiplegic adults.

An analysis of the correlation of lesion size, localization and behavioral effects in 283 published studies of cortical and subcortical lesions in old-world monkeys

The present article evaluates the quality and magnitude of the effects of lesion size and location and their interaction, on the behavioral performance of old world monkeys by a quantitative comparison of 283 published studies. The results indicate that lesion size alone is a poor predictor of the behavioral performance of monkeys, as opposed to Lashley's work in rats. Lesion location is a reliable predictor of the behavioral performance for brain regions thought to be primarily involved in a specific behavior; however, similar behavioral effects, although less reliable, can be observed for many different lesion loci, suggesting a specialized and a holistic brain functioning to be working at the same time. Some lesion loci are, in sharp contrast to current hypotheses about functional localization in the brain, not associated with impairments, but with significant improvements of a specific behavior. For such lesion loci the correlation of lesion size and behavioral performance may yield significant positive relationships (that is, increasing behavioral improvement with increasing lesion size); these relationships are contrasted by the significant negative relationships obtained for lesions of brain regions thought to be primarily involved in a given behavior. Thus, the lesion size may be a good predictor of the behavioral performance, depending on the lesion location and on the behavior under measurement. The behaviors analysed in this study were discrimination or delayed reaction or delayed matching-to-sample. The former two behaviors involve habit-like learning and are thought to be mediated by corticostriate functional pathways in the brain and the latter behavior implies the learning of single events, being thought to be mediated by corticolimbic functional pathways in the brain. Improved performances were observed for habit-like behaviors after lesions of brain regions (lateral frontal, premotor/motor, parietal, inferotemporal cortex, amygdala and fornix) being not primarily involved in a given behavior but possibly being able to inhibit the corticostriate pathways. Interestingly, lesions of subareas of the neostriatum were found to cause impairments in habit-like behaviors presumably being processed via these subareas (e.g. head of the caudate nucleus and delayed reaction), but to cause significant improvements in other behaviors (e.g. head of the caudate nucleus and visual discrimination). Thus, it may be concluded that diverse systems of functionally interconnected brain regions may maintain reciprocal inhibitions, with the result that a lesion within one system not only leads to a loss of one behavior, but in addition leads to a modification, may be a facilitation, of another behavior.(ABSTRACT TRUNCATED AT 400 WORDS)

Functional recovery after limbic lesions in monkeys

Ten monkeys received lesions of either the hippocampus, or the amygdala and hippocampus, or the anterior and medial thalamus (each group with two monkeys), or of all these structures together with additional septal lesions (four monkeys). Postoperatively, the monkeys were trained in tasks of visual and spatial reversal, several concurrent object discriminations, delayed nonmatch-to-sample, and in an angle threshold discrimination task. Their performance was compared to that of five healthy or sham-operated control monkeys. The single- or double-lesioned monkeys were impaired in the delayed nonmatch-to-sample task and the angle threshold discrimination, whereas monkeys with five-fold lesions were unimpaired in these tasks. Correlations between brain volume loss and behavioral performance indicated negative coefficients for the delayed nonmatch-to-sample task ("delays": rs = -.59, "lists": rs = -.20) and the angle threshold discrimination (rs = -.60). It is concluded that monkeys with massive limbic lesions display a more effective postlesion reorganization than monkeys with smaller limbic lesions; however, reliability of this effect must be proved by future work with a larger sample. Furthermore, the missing impairments of massively lesioned monkeys especially in the delayed nonmatch-to-sample task also indicate that the limbic targets lesioned here may not be as exclusively involved in mnemonic information processing as suggested earlier.

Neglect following unilateral ablation of the caudal but not the rostral portion of medial agranular cortex of the rat and the therapeutic effect of apomorphine

The medial agranular cortex (AGm) of the rat is often considered analogous to the frontal eye field (FEF) of the monkey. However, recent anatomical, physiological, and behavioral evidence indicates that, while the caudal portion of AGm may indeed be an analog of the primate FEF, the rostral portion of AGm may be more similar to the primate supplementary motor area. The current study examined the effects of unilateral ablation of both the rostral and caudal components of AGm on the ability to orient to unilaterally presented stimuli. As expected, lesions of caudal but not rostral AGm resulted in a severe unilateral neglect of stimuli characteristic of rats with lesions of the entire rostral-caudal extent of AGm and of monkeys with FEF lesions. Caudal AGm operates also had more severe neglect than a group of rats from a previous study with larger AGm lesions which damaged the caudal portion of AGm to varying degrees. In addition, a second study showed the dopamine agonist apomorphine to have an acute dose-dependent therapeutic effect on the neglect resulting from caudal AGm ablation similar to that seen in animals with ablation of the entire rostral-caudal extent of AGm.

Neural plasticity in vivo: opioid sensitivity of memory develops gradually after a septal lesion

Neuronal plasticity can manifest itself in alterations in the sensitivity of memory to the effects of drugs. After the production of a brain lesion, the memory processing of a passive-avoidance task in mice gradually becomes sensitive to the effect of morphine, i.e., an improvement in retention performance is seen after 6 weeks, but not after 1 or 2 weeks. The results presented demonstrate that, even if they lead to no discernible changes in behaviour, plastic processes can still be detected by means of behavioural tests.

Learning ability in young rats with single and double lesions to the "general learning system"

Previous lesion studies suggest that the dorsal caudatoputamen (DCP), globus pallidus, ventrolateral thalamus (VLT), substantia nigra, ventral tegmental area, superior colliculus (SC), median raphe, and pontine reticular formation are components of the general learning system (GLS) of the rat brain. The current study attempted to determine whether bilateral lesions to two components of the GLS (DCP/VLT, DCP/SC or VLT/SC) would produce greater deterioration of learning ability than bilateral lesions to only one component (DCP, VLT or SC). In all combinations examined, a second lesion added to the first led to a significantly greater learning decrement on a series of spatial reversal problems than that associated with the first lesion alone. These results are compatible with the view that the foregoing structures are elements of the same functional system concerned either directly or indirectly with general learning ability.