Structures and functions of the post-mortem brain: an experimental evaluation of the residual properties of fixed neural tissues

Abstract

Does brain function irreversibly cease after death? Billions of years of evolution and hundreds of thousands of years of human development have inculcated within us an intuition that death is a deep pit from which thoughts and behaviour cannot emerge. This dissertation serves to challenge the assumption of neurofunctional loss after death by employing modern technology to observe alternative mechanisms by which information can be processed by fixed, post-mortem neural tissues. The central aim of the thesis was to measure periodic, electric potential differences (μV) characteristic of the psychological definition of “response” within neuroanatomical loci while the fixed tissues were exposed to patterned current, complex electromagnetic fields, chemical probes, and other experimental conditions. The findings presented here show that fixed post-mortem tissues express regional, electrical anisotropies which can be modulated by various applications of electrochemical energy and that the areas surrounding the hippocampus are most responsive. We show that neuropathology secondary to repeated and protracted seizure activity can be detected in post-mortem rat brains with coupled depressions of low-frequency signal periodicities. Our findings demonstrate that injections of current into coronal sections of fixed human brain tissue are most potent when patterned to simulate neuronal spike-trains and the dominant frequency of the equivalent living tissue subsection. We also show that fixed, post-mortem brain tissues act as electromagnetic filters, expressing signals non-randomly and preferentially within the right cerebral hemisphere. Further findings indicate that receptor agonist-antagonist probes (e.g., glutamate and ketamine) as well as other chemical applications can induce regional electrical responses as well as habituation-type phenomena over repeated exposure. iv These responses are paired and can be inversely related to photon emission from the tissue proper as inferred by photomultiplier tube measurements. The bases of the electrochemical responses are thought to be due to phenomena associated with pH and ionic gradients in general as inferred by our experiments with post-mortem rat brains. The aforementioned experimental results are then synthesized to produce a working hypothesis upon which further research can be based. We conclude that the brain’s structure-function relationship is sufficient to elicit post-mortem responses characteristic of a composite material of otherwise unknown potential.