[Post-contusional thalamic-autonomous focus attacks].

Several decades of research into the function of the frontal lobes in brain-damaged patients, and more recently in intact individuals using function brain imaging, has delineated the complex executive functions of the frontal cortex. And yet, the mechanisms by which the brain achieves these functions remain poorly understood. Here, we present a computational model of the role of the prefrontal cortex (PFC) in controlled memory use that may help to shed light on the mechanisms underlying one aspect of frontal control: the development and deployment of recall strategies. The model accounts for interactions between the PFC and medial temporal lobe in strategic memory use. The PFC self-organizes its own mnemonic codes using internally derived performance measures. These mnemonic codes serve as retrieval cues by biasing retrieval in the medial temporal lobe memory system. We present data from three simulation experiments that demonstrate strategic encoding and retrieval in the free recall of categorized lists of words. Experiment 1 compares the performance of the model with two control networks to evaluate the contribution of various components of the model. Experiment 2 compares the performance of normal and frontally lesioned models to data from several studies using frontally intact and frontally lesioned individuals, as well as normal, healthy individuals under conditions of divided attention. Experiment 3 compares the model's performance on the recall of blocked and unblocked categorized lists of words to data from Stuss et al. (1994) for individuals with control and frontal lobe lesions. Overall, our model captures a number of aspects of human performance on free recall tasks: an increase in total words recalled and in semantic clustering scores across trials, superiority on blocked lists of related items compared to unblocked lists of related items, and similar patterns of performance across trials in the normal and frontally lesioned models, with poorer overall performance of the lesioned models on all measures. The model also has a number of shortcomings, in light of which we suggest extensions to the model that would enable more sophisticated forms of strategic control.

Brain Injuries↗

PubMed2003

Hypothermia in the management of traumatic brain injury. A systematic review and meta-analysis.

OBJECTIVE: Brain injury remains the leading cause of death in cases of trauma in North America and Europe. This article critically appraised and summarised all published and peer-reviewed, randomised, controlled trials of the use of hypothermia in traumatic brain injury. DESIGN: To be included, a study had to be a published, randomised, controlled trial of the use of hypothermia in the management of traumatic brain injury. Pooling of data and meta-analysis of results occurred. SETTING: Conducted at a tertiary level Canadian teaching hospital. PATIENTS AND PARTICIPANTS: Patients were combined from eight randomised, controlled trials to generate a population of 748 severely head-injured patients. MEASUREMENTS AND RESULTS: Eight studies provided data on the efficacy of hypothermia in the management of traumatic brain injury. The pooled odds ratio of mortality in the hypothermic group was 0.81 (95%CI =0.59-1.13, p=0.22). The OR of a poor neurological outcome (GOS 1,2 or 3) was 0.75 (95% CI=0.56-1.01, p=0.06). The odds ratio for pneumonia in the normothermic group was 0.42 (95%CI =0.25-0.70, p=0.001). CONCLUSIONS: Although meta-analysis suggests that iatrogenic hypothermia may confer a marginal benefit in neurological outcome, there does not appear to be clear evidence of lower mortality rates in unselected traumatic brain injury patients. Prolonged hypothermia may confer a benefit, particularly in patients with elevated intracranial pressure refractory to conventional manipulations. Conclusions regarding the use of hypothermia are controversial and not strongly supported by the available evidence.

Brain Injuries↗