2                                                                                                Brainwave Connections                                                                    Year’s End 2006
Text Box: The brain is a hyperconnected system. It contains on the order of 10 billion neurons, each of which can have hundreds or thousands of connections to other neurons. The brain depends on dynamically managing trillions of connections, to regulate the interactions between all of its parts (Calvin 1995, Sejnowski 2004) How are all of these connections managed toward useful ends? The key lies in the ability of the network to selectively enable or disable connections, based upon a simple model of excitation and inhibition. Connectivity refers to the mechanism by which parts of a system work together, via communication and control. Connectivity results when information is shared between parts, and used in a coherent manner to produce sensation, perception, decision-making, and behavior. One of the most important functions in the brain is that of inhibition This is true on the microscopic level, and also on the macroscopic level. Early sensory experiences have profound effects on the fine structural and functional organization of the brain. .(e.g. Jiao 2006). A great deal of this adaptation takes the form of creating and shaping connections between neuronal assemblies, mediated by the dynamic balance of excitatory and inhibitory connections in the network. Text Box: In the words of Sir Charles Sherrington (1933), The dictum that life’s aim is an act not a thought must be modified to admit that, often, to refrain from an act is no less an act than to commit one, because inhibition is coequally with excitation a nervous activity. When we examine the synaptic inputs a typical pyramidal cells in the cortex or even in the thalamus, we see that in excess of 90% of the inputs to a particular cell may be inhibitory. Only a small fraction are typically excitatory, inasmuch as most neurons are inherently excitable by virtue of their membrane properties, and need to be “sedated,” more than they need to be even more excited. A great deal of inhibition is in the form of collateral inhibition. This takes place when collateral fibers in a pathway inhibit each other whenever information is being sent. As a result of this inhibition, neuronal bundles and tracts are able to transmit information with sharpness, fidelity, and high resolution. As an example of the power of this fidelity, consider that the auditory nerve can respond with action potentials to a deflection in the basilar membrane of no more than 1 Angstrom, which is the diameter of a hydrogen atom. This reveals unimaginable acuity in the physiological and neuronal mechanisms at work. Similarly, the eye is capable of seeing a candle light at 12 miles, which Text Box: corresponds to a stimulus rate of one photon per second. If neuronal signals were allowed to mix and scramble, such acuity and precision would not be possible. Without inhibition at a cellular level, brain activity would degenerate into pure chaos including seizure activity, devoid of purposeful control or meaning. At the larger systems level, inhibition is an important component to brain function. Jeffrey Carmen has observed that the reaction of a chicken to having its head removed is to flap its wings, run about, and attempt to squawk, before finally expiring. The function of the chicken’s brain is more to inhibit automatic mechanisms than to instigate specific behaviors. I the same way, Carmen refers to the frontal lobes of the human brain as the “chicken’s brain” of the entire brain. That is, the frontal lobes spend the majority of their activity inhibiting activities, including behaviors, that the rest of the brain is all too ready to undertake. This explains why dysfunction of the frontal lobes often results in disorders characterized by a lack of inhibition of thoughts or behaviors that are detrimental to the individual. When EEG training is performed at the level of brain connectivity and communication, it becomes possible to address directly the relative excitation and inhibition, but particularly the inhibition, of neuronal Text Box: Connectivity, Inhibition, and Path-Specific

The dictum that life’s aim is an act not a thought must be modified to admit that, often, to refrain from an act is no less an act than to commit one, because inhibition is coequally with excitation a nervous activity.

 

-Sir Charles Sherrington

Article by:

Thomas F. Collura, Ph.D., P.E.

 

Computer reconstruction of four pyramidal neurons    from somatosensory cortex layer 5.

 

(Image by Dr. Qian-Qan Sun, University of Wyoming)