Neural Compensations After Lesion of the Cerebral Cortex

Functional improvement after cortical injury can be stimulated by various factors including experience, psychomotor stimulants, gonadal hormones, and neurotrophic factors. The, timing of the administration of these factors may be critical, however. For example, factors such as gonadal hormones, nerve growth factor, or psychomotor stimulants may act to either enhance or retard recovery, depending upon the timing of administration. Nicotine, for instance, stimulates recovery if given after an injury but is without neuroprotective effect and may actually retard recovery if it is given only preinjury. A related timing problem concerns the interaction of different treatments. For example, behavioral therapies may act, in part, via their action in stimulating the endogenous production of trophic factors. Thus, combining behavioral therapies with pharmacological administration of compounds to increase the availability of trophic factors enhances functional outcome. Finally, anatomical evidence suggests that the mechanism of action of many treatments is through changes in dendritic arborization, which presumably reflects changes in synaptic organization. Factors that enhance dendritic change stimulate functional compensation, whereas factors that retard or block dendritic change block or retard compensation

Population coding in sparsely connected networks of noisy neurons

This study examines the relationship between population coding and spatial connection statistics in networks of noisy neurons. Encoding of sensory information in the neocortex is thought to require coordinated neural populations, because individual cortical neurons respond to a wide range of stimuli, and exhibit highly variable spiking in response to repeated stimuli. Population coding is rooted in network structure, because cortical neurons receive information only from other neurons, and because the information they encode must be decoded by other neurons, if it is to affect behavior. However, population coding theory has often ignored network structure, or assumed discrete, fully connected populations (in contrast with the sparsely connected, continuous sheet of the cortex). In this study, we modeled a sheet of cortical neurons with sparse, primarily local connections, and found that a network with this structure could encode multiple internal state variables with high signal-to-noise ratio. However, we were unable to create high-fidelity networks by instantiating connections at random according to spatial connection probabilities. In our models, high-fidelity networks required additional structure, with higher cluster factors and correlations between the inputs to nearby neurons

Millisecond-Timescale Local Network Coding in the Rat Primary Somatosensory Cortex

Correlation among neocortical neurons is thought to play an indispensable role in mediating sensory processing of external stimuli. The role of temporal precision in this correlation has been hypothesized to enhance information flow along sensory pathways. Its role in mediating the integration of information at the output of these pathways, however, remains poorly understood. Here, we examined spike timing correlation between simultaneously recorded layer V neurons within and across columns of the primary somatosensory cortex of anesthetized rats during unilateral whisker stimulation. We used Bayesian statistics and information theory to quantify the causal influence between the recorded cells with millisecond precision. For each stimulated whisker, we inferred stable, whisker-specific, dynamic Bayesian networks over many repeated trials, with network similarity of 83.3±6% within whisker, compared to only 50.3±18% across whiskers. These networks further provided information about whisker identity that was approximately 6 times higher than what was provided by the latency to first spike and 13 times higher than what was provided by the spike count of individual neurons examined separately. Furthermore, prediction of individual neurons' precise firing conditioned on knowledge of putative pre-synaptic cell firing was 3 times higher than predictions conditioned on stimulus onset alone. Taken together, these results suggest the presence of a temporally precise network coding mechanism that integrates information across neighboring columns within layer V about vibrissa position and whisking kinetics to mediate whisker movement by motor areas innervated by layer V

Neural changes in forelimb cortex and behavioural development

x, 132 leaves : ill. ; 28 cm.Neural changes in the forelimb cortex were studied at Postnatal (P) 10, 15, 20, 25, 30, and 100 days. Six biological markers of brain development, cortical thickness, Layer III pyramidal cell morphology, glial fibrillary acidic protein (GFAP), myelination, c-fos activity and Acetylcholinesterase (AChE) were correlated with the behavioural development of reaching, bimanual coordination, postural adjustment, and defensive feeding behaviours. The behaviours were filmed from P15 until P30 and then also in adulthood. For the behaviours there was a gradual development of the skilled patterns of paw and digit use seen in adults as well as in the patterns of movements in postural adjustment, carry behaviours and dodging and robbing type behaviours. The development of the adult patterns of movement were correlated to the morphological and biochemical changes in the cortex. The results suggest that the maturation of skilled movements depends upon anatomical and neurochemical maturation of the neocortex as well as upon learning

Experimental stimulation as a treatment for early brain damage

v, [14], 208 leaves : ill. ; 28 cm.The current work explores the therapeutic potential of experiential treatments for enhancing functional recovery and anatomical change after early brain damage. Normal rats and rats with perinatal cortical lesions (P2 or P7) were exposed to one of the following treatments: complex housing as juveniles, complex housing as adults, prenatal tactile stimulation, postnatal tactile stimulation, or postnatal handling (removal from the nest with no additional stimulaion). Behavior was assessed in adulthood the Morris water task and the Whishaw reaching task. There were sex differences in the details of the effect of experience on both behavioral recovery and brain morphology. For both sexes treatments initiated prior to or immediately after brain injury were most effective in improving functional outcome. This was correlated with changes in dendritic arborization and Acetylcholinesterase staining. The results suggest that behavioral treatments can be used to stimulate functional recovery after early brain injury

Perinatal experience alters brain development and functional recovery after cerebral injury in rats

xxi, 221 leaves : ill. ; 28 cm.Brain damage in the first week of life is behaviorally and anatomically devastating for a rat. I investigated the use of pre- and/or postnatal experience as interventions that might improve the outcomes in rats with postnatal day 4 (P4) frontal cortex lesions. Prenatal maternal tactile stimulation or maternal complex housing facilitated recovery in P4 lesion animals and produced changes in brain organization. Post-lesion tactile stimulation also was found to be beneficial possibly via experience dependent changes in FGF-2 expression. Levels of FGF-2 were increased in both skin and brain after tactile stimulation and correlated with behavioral and anatomical changes. Direct post-lesion administration of FGF-2 had similar effects. These results are the first demonstration that prenatal experience can be prophylactic for postnatal brain injury and that behavioral experience can act on brain organization via enhanced trophic factor expression originating in skin