Recovery from electroencephalographic slowing and reduced evoked potentials after somatosensory cortical damage in cats

A working model for hypothermic neuroprotection

Therapeutic hypothermia significantly improves survival without disability in near-term and full-term newborns with moderate to severe hypoxic-ischaemic encephalopathy. However, hypothermic neuroprotection is incomplete. The challenge now is to find ways to further improve outcomes. One major limitation to progress is that the specific mechanisms of hypothermia are only partly understood. Evidence supports the concept that therapeutic cooling suppresses multiple extracellular death signals, including intracellular pathways of apoptotic and necrotic cell death and inappropriate microglial activation. Thus, the optimal depth of induced hypothermia is that which effectively suppresses the cell death pathways after hypoxia-ischaemia, but without inhibiting recovery of the cellular environment. Thus mild hypothermia needs to be continued until the cell environment has recovered until it can actively support cell survival. This review highlights that key survival cues likely include the inter-related restoration of neuronal activity and growth factor release. This working model suggests that interventions that target overlapping mechanisms, such as anticonvulsants, are unlikely to materially augment hypothermic neuroprotection. We suggest that further improvements are most likely to be achieved with late interventions that maximise restoration of the normal cell environment after therapeutic hypothermia, such as recombinant human erythropoietin or stem cell therapy.

Post-Traumatic Neural Depression and Neurobehavioral Recovery after Brain Injury

There are an estimated 2 million traumatic brain injuries (TBIs) each year in the United States, making the yearly incidence eight times greater than that of breast cancer and 34 times greater than HIV/AIDS. Still, it remains a "silent epidemic" because TBI results in persistent neurobehavioral impairment, without necessarily imparting a physical scar. The present review is a comparative analysis of TBI research, both basic and applied, outlining the evidence that at least one component of the brain's innate response to insult (e.g., post-traumatic neural depression) is sufficiently well understood to be the target of additional clinical studies and therapeutic strategy development.

Interhemispheric differences of sensory hand areas after monohemispheric stroke: MEG/MRI integrative study

Seventeen clinically stabilized monohemispheric stroke patients were studied in order to investigate the chronic topographical modifications induced on primary sensory cortical hand areas by a monohemispheric stroke within the middle cerebral artery territory. Magnetoencephalographic (MEG) localization of the cortical areas activated following electrical separate stimulation of the median nerve, thumb, and little fingers was integrated with magnetic resonance imaging. Spatial localization of Equivalent Current Dipoles (ECDs) of the short-latency cortical responses generated in primary sensory cortices, "hand area" (distance between 1st and 5th digits ECDs), interhemispheric differences of such parameters, as well as of somatosensory-evoked fields waveshapes were investigated and compared with a control population. Lesions involving the cortico-subcortical areas receiving sensory input from the hand induced excessive asymmetry of MEG spatial parameters and response morphology between the unaffected (UH) and the affected hemisphere (AH). "Hand area" was significantly larger on AH in 20% of cases after a subcortical, and in 13% after a cortical, lesion. Responses from AH were excessively delayed in 20% ECDs. Interhemispheric ECDs strength differences were larger than normal in 25% of cases after both types of lesions; the strength in the AH being enlarged after all cortical, and only 24% of subcortical strokes. In a significant percentage of monohemispheric strokes, excessive interhemispheric differences were found between AH and UH, suggesting that brain areas outside the normal boundaries and usually not reached by a dense sensory input from the opposite hand and fingers may act as somatosensory "hand" centers. Correlation analysis between clinical outcome and cortical reorganization in the AH suggests that this mechanism is linked with hand sensorimotor recovery.

Phenobarbital administration directed against kindled seizures delays functional recovery following brain insult

Anti-convulsant drug administration or recurrent seizures can impact functional recovery following brain insult. The nature of that impact depends on a variety of factors, including timing of drug administration and drug mechanism of action, as well as seizure number, timing, and severity. The objective of this study was to determine the functional consequences of anti-convulsant administration directed against seizure activity in brain-damaged animals. To this end, phenobarbital was coupled with daily electrical kindling of the amygdala beginning 48 h after a unilateral anteromedial cortex lesion. Recovery from somatosensory deficits was assessed, as was regional atrophy and basic fibroblast growth factor (bFGF) expression. Animals receiving phenobarbital prior to daily kindling failed to recover within 2 months of testing. In contrast, animals receiving saline prior to kindling as well as phenobarbital-treated non-kindled animals recovered within 2 months after the lesion. Though the exact mechanisms underlying these behavioral phenomena remain uncertain, patterns of bFGF expression among the groups provide some insight. Taken together, results from the present study suggest that anti-convulsant drug administration directed against subclinical seizure activity can be more detrimental to functional recovery than seizures alone or anti-convulsant drug treatment after seizure activity has occurred.

Hypothesized neural dynamics of working memory: several chunks might be marked simultaneously by harmonic frequencies within an octave band of brain waves

The capacity of working memory (WM) for up to about seven simple items holds true both for humans and other species, and may depend upon a common characteristic of mammalian brains. This paper develops the conjecture that each WM item is represented by a different brain wave frequency. The binding-by-synchrony hypothesis, now being widely investigated, holds that the attributes of a single cognitive element cohere because electroencephalogram (EEG) synchrony temporarily unifies their substrates, which are distributed among different brain regions. However, thought requires keeping active more than one cognitive element, or WM "chunk," at a time. If there is indeed a brain wave frequency code for cognitive item-representations that are copresent within the same volume of neural tissue, the simple mathematical relationships of harmonies could provide a basis for maintaining distinctness and for orderly changes. Thus, a basic aspect of music may provide a model for an essential characteristic of WM. Music is a communicative phenomenon of "intermediate complexity," more highly organized than the firing patterns of individual neurons but simpler than language. If there is a distinct level of neural processing within which the microscopic physiological activity of neurons self-organizes into the macroscopic psychology of the organism, it might require such moderate complexity. Some of the obvious properties of music--orderly mixing and transitions among limited numbers of signal lines-are suggestive of properties that a dynamic neural process might need in order to organize and reorganize WM markers, but there are a number of additional, nonobvious advantageous properties of summating sinusoids in music-like relationships. In particular, harmonies register a stable periodic signal in the briefest possible time. Thus, the regularity of summating sinusoids whose frequencies bear harmony ratios suggests a particular kind of tradeoff between parallel and serial processing. When there are few copresent waves, at EEG frequencies, this sort of parallel coding retains behaviorally meaningful brief periods. A necessary companion hypothesis is that the brain wave frequencies underlying WM are confined to a single octave; that is, the upper and lower bounds of the band are in the ratio of 2:1. This hypothesized restriction, suggested by an empirical property of EEG bands that has been widely reported but rarely commented upon, has the important property of precluding spurious difference rhythms. A restriction to an octave, of "harmonious" frequency-markers for WM items, also seems consistent with a great deal of behavioral data suggesting that WM comprises a rapidly fading trace process in which only up to three or four item-representations are strongly activated simultaneously. There is also an additional, sequential renewal-or-revision process, within which up to another three or four items are being actively refreshed by rehearsal or replaced. Such serial processing may involve a less stringent octave band crowding problem.

Plasticity of primary somatosensory cortex paralleling sensorimotor skill recovery from stroke in adult monkeys

Adult owl and squirrel monkeys were trained to master a small-object retrieval sensorimotor skill. Behavioral observations along with positive changes in the cortical area 3b representations of specific skin surfaces implicated specific glabrous finger inputs as important contributors to skill acquisition. The area 3b zones over which behaviorally important surfaces were represented were destroyed by microlesions, which resulted in a degradation of movements that had been developed in the earlier skill acquisition. Monkeys were then retrained at the same behavioral task. They could initially perform it reasonably well using the stereotyped movements that they had learned in prelesion training, although they acted as if key finger surfaces were insensate. However, monkeys soon initiated alternative strategies for small object retrieval that resulted in a performance drop. Over several- to many-week-long period, monkeys again used the fingers for object retrieval that had been used successfully before the lesion, and reacquired the sensorimotor skill. Detailed maps of the representations of the hands in SI somatosensory cortical fields 3b, 3a, and 1 were derived after postlesion functional recovery. Control maps were derived in the same hemispheres before lesions, and in opposite hemispheres. Among other findings, these studies revealed the following 1) there was a postlesion reemergence of the representation of the fingertips engaged in the behavior in novel locations in area 3b in two of five monkeys and a less substantial change in the representation of the hand in the intact parts of area 3b in three of five monkeys. 2) There was a striking emergence of a new representation of the cutaneous fingertips in area 3a in four of five monkeys, predominantly within zones that had formerly been excited only by proprioceptive inputs. This new cutaneous fingertip representation disproportionately represented behaviorally crucial fingertips. 3) There was an approximately two times enlargement of the representation of the fingers recorded in cortical area 1 in postlesion monkeys. The specific finger surfaces employed in small-object retrieval were differentially enlarged in representation. 4) Multiple-digit receptive fields were recorded at a majority of emergent, cutaneous area 3a sites in all monkeys and at a substantial number of area 1 sites in three of five postlesion monkeys. Such fields were uncommon in area 1 in control maps. 5) Single receptive fields and the component fields of multiple-digit fields in postlesion representations were within normal receptive field size ranges. 6) No significant changes were recorded in the SI hand representations in the opposite (untrained, intact) control hemisphere. These findings are consistent with "substitution" and "vicariation" (adaptive plasticity) models of recovery from brain damage and stroke.

On the reorganization of sensory hand areas after mono-hemispheric lesion: a functional (MEG)/anatomical (MRI) integrative study

The topography of primary sensory cortical hand area following a monohemispheric lesion (sudden = stroke; progressive = neoplasm) was investigated in relationship with clinical recovery of sensorimotor deficits. Twenty seven patients with monohemispheric lesions were studied in a clinically stabilized condition. Functional informations from magnetoencephalography (MEG) were integrated with anatomical data from magnetic resonance imaging (MRI). MEG localizations of the neurons firing at early latencies in primary sensory cortex after separate stimulation of median nerve, thumb and little fingers of each hand were carried out. Characteristics of cerebral equivalent current dipoles (ECDs) activated by each contralateral stimulation, the 'hand extension' (i.e., the distance in millimetres between ECDs of first and fifth digits), as well as interhemispheric differences of the tested parameters were investigated. Finally, ECDs' locations were integrated with MRI. Lesions involving cortical (C) or subcortical (s.c.) areas receiving sensory input from the hand were often combined to increase interhemispheric asymmetry of the tested parameters (22% for C and 49% for s.c. lesions). This might be due to an activation of neuronal districts which in the affected hemisphere (AH) differ from those normally activated in the unaffected hemisphere (UH) and in the control population. Moreover, the 'hand extension' was enlarged on the AH--more frequently after a SC lesion--mainly due to a medial shift of the little finger ECD, combined to a tendency of both finger ECDs to shift frontally. After a C lesion, responses from the AH were often stronger than normal. Spatial reorganizations were also seen in the UH (7% of C and 14% of SC lesions). 'Hand extension' in the UH was selectively enlarged for the P30m only when combined with a similar enlargement in the AH. Significant interhemispheric asymmetries due to neuronal reorganization in the AH were associated with worse clinical outcomes compared to patients without asymmetries.

Electrophysiological transcortical diaschisis after cortical photothrombosis in rat brain

BACKGROUND AND PURPOSE

The severity of functional deficits after a cortical infarction often does not correlate with lesion size. The stroke may affect pathways connecting to distant brain regions and therefore may also alter the function of remote parts of the cortex. Remote changes in electric activity, blood flow, and metabolism are called diaschisis. In the present study we addressed the question of whether in brain areas contralateral to a photochemically induced cortical infarction alteration of excitability can be observed as an indication of the effects of diaschisis.

METHODS

We induced focal lesions in the sensory area at the border of the motor and occipital cortices by injecting the photosensitizing dye rose bengal and illuminating the skull stereotaxically. Seven days after induction of photothrombosis, electrophysiological recordings were obtained with standard methods from 400-microns-thick neocortical coronal slices. As an indication of inhibition we used a paired-pulse stimulus protocol and calculated a ratio of the amplitudes of the second versus the first excitatory postsynaptic potential.

RESULTS

In lesioned animals we found a significant increase of the ratio over a wide zone of the neocortex, both ipsilateral and contralateral, compared with unlesioned animals.

CONCLUSIONS

Our results suggest that a neocortical infarction leads to hyperexcitability not only in its direct vicinity but also in the contralateral hemisphere. Such hyperexcitability may contribute to increased activation of contralateral brain areas and to functional reorganization after stroke.

Kindled seizures during a critical post-lesion period exert a lasting impact on behavioral recovery

The present study was undertaken to assess the effects of amygdala kindling on behavioral recovery following unilateral frontal cortex damage in rats. Daily electrical stimulation of the amygdala began 48 h after lesion and continued until all animals had a single Stage 5 seizure. When amygdala kindled seizure activity ratable as Stage 0 occurred within the first 6 days after lesion, animals recovered from somatosensory asymmetries in approximately 3 weeks. In contrast, kindled animals that experienced Stage 1 seizure activity within the first 6 days after lesion failed to recover from somatosensory deficits in 4 months of testing. Differences in rate of recovery could not be accounted for by lesion size or placement. These data support the notion that not only is there a 'critical period' after brain damage during which the recovery process is vulnerable to seizure activity, but the type of kindled seizure that is experienced during that time ultimately determines how recovery is affected.

Disruption of behavioral recovery by the anti-convulsant phenobarbital

The effects of the anti-convulsant phenobarbital on recovery of function was assessed. Phenobarbital, which is frequently administered to humans after brain injury, was injected for 7 days beginning 48 h after unilateral cortex lesions in rats. Recovery from somatosensory deficits was significantly delayed in phenobarbital treated animals. These results provide additional evidence that anti-convulsants interfere with recovery when administered after brain damage.

Cortical microstimulation thresholds adjacent to sensorimotor cortex injury

The initial severe contralateral impairment of motor function after unilateral damage to a portion of sensorimotor (SM) cortex lessens within a few weeks after injury. In this study, two hypotheses proposed to explain recovery of behavioral function after cortical injury were tested: (1) Intact cortex adjacent to the injury reorganizes to take over the function of the destroyed area. (2) Intact SM cortex adjacent or connected to the injured area undergoes a transient shock (diaschisis), and as this dissipates, some behavioral recovery occurs. Using microstimulation of the cortex of the adult rat, movements evoked from areas near cortical injuries were studied at various times after undercut laceration, contusion, or suction ablation of an area of SM cortex. Stimulation areas were compared to those obtained from uninjured control animals and to the contralateral uninjured hemisphere. No evidence was obtained for any reorganization of stimulated motor responses in the injured hemisphere even in animals followed for as long as 475 days postinjury, suggesting other mechanisms underlying functional recovery. In intact cortex at some distance from contusion and laceration injuries, there was a marked elevation of thresholds to evoke movements that returned to normal by 9-15 days postinjury. Some intact hindlimb responses were observed after contusion injury that were absent in animals after 15 days postinjury, indicating a slow-growing lesion after this type of trauma. Surprisingly, no elevation in thresholds was noted for ablation injuries up to the edge of the cavity at any time postinjury, indicating that threshold changes near the boundary may be uncorrelated with functional recovery.

Failure to find electrophysiological correlates of chronic neuroleptic-induced oral dyskinesias in cats: somatosensory and substantia nigra evoked potentials, electroencephalogram, and caudate spindles

Each of nine cats was prepared with 30 chronically implanted stainless steel gross electrodes in cortex, basal ganglia and other brain structures. Measurements were taken for 0.5-11.5 months of baseline, chronic daily administration of chlorpromazine, and withdrawal. In most cases there was also a second cycle of drug administration and withdrawal. Although we observed dramatic, persistent increases in licking behavior, suggestive of tardive dyskinesia, consistent correlated patterns were not observed in somatosensory or substantia nigra evoked potentials, electroencephalogram, or spindling evoked in cortex by caudate stimulation.

Responses to cortical injury: II. Widespread depression of the activity of an enzyme in cortex remote from a focal injury

As a part of a broader study of the reaction of the brain to injury, we report here an interesting loss of the activity of an enzyme in areas quite remote from the site of direct injury. At 36 h following a laceration or contusion injury to the hindpaw area of the motor cortex, a peculiar loss of staining for the enzyme alpha glycerophosphate dehydrogenase (alpha-GPDH) was noted. alpha-GPDH activity was markedly depressed in cortical layers II and III throughout the hemisphere on the side of the injury. The depression of alpha-GPDH activity extended far laterally across the rhinal fissure into the pyriform cortex. The decrease in alpha-GPDH staining was prominent 4 days after the injury: however, the staining pattern had returned to normal at 9 days. Enzyme changes in animals lesioned in the occipital cortex paralleled that seen in animals with a lesion in the motor cortex. Animals which had received an undercut lesion in the motor cortex 56 days earlier were contused in the occipital cortex. The old injury site presented the same sequelae of changes as seen in other lesioned animals. Additionally, a suction ablation injury involving only a small part of motor cortex resulted in the same widespread reduction of staining for alpha-GPDH in layers II and III. The derangement in energy metabolism suggests that cells in layers II and III of the cerebral cortex may be particularly vulnerable to perturbations induced by cortical trauma. These findings may be related to the diffuse and transient functional losses observed after head injury in man.

Does the brain actively maintain itself?

All living systems have special mechanisms for combatting entropy; however, the brain has dimensions of organized complexity beyong those manifest in the anatomical structure and physiology of the rest of the body. Reasons are given in support of the notion that the brain therefore must have a special, intrinsic "homeostatic" system for its information bearing structures, and, further, that slow electroencephalographic activity has properties which might make it useful for such an order-maintaining function. Recovery from brain damage is hypothesized to be a byproduct of this process, which may involve a cruder sort of information processing than occurs with such functions as perception and learning. Synchronized EEG activity may be adequate to handle this sort of information processing. Speculations are offered about possible mechanics, on the neuronal level, of slow wave participation in plasticity; for example, one such suggestion is based on findings that electrical fields can influence cellular orientation. The methodology of discovering the distribution within the brain of the hypothetical maintenance system is discussed briefly.