Patent No. 5522863 Pulsating behavior monitoring and modification system for neural networks

 

Patent No. 5522863

Pulsating behavior monitoring and modification system for neural networks (Spano, et al., Jun 4, 1996)

Abstract

The pulsating behavioral activity of a neural network such as that embodied n a brain tissue slice is monitored by measurement of intervals between spontaneous events to identify the presence of a chaotic regime and determine by real-time calculation a waiting time for electrical pulse intervention pursuant to a behavioral modifying program having a control or anti-control strategy.

Notes:

BACKGROUND OF THE INVENTION

Many activities of an apparently random nature have been found to exhibit a deterministic phenomenon known as chaos, including but not limited to irregular pulsating behavior of living animal tissue. Recently, a strategy was developed tending to control a non-linear dynamic system in which a chaotic regime occurs. The critical features of the chaos phenomenon believed to make such control possible are short term predictability and extreme sensitivity of chaotic systems to perturbances of their initial conditions. A key to the control strategy lies in the fact that a chaotic system includes an infinite number of unstable periodic motions and never remains very long in any of such unstable motions, but continually switches from one periodic motion to another to thereby give an appearance of randomness. The chaos control strategy involves measurement of the current system parameter and identification of an unstable fixed point of interest representative of a system state plotted along with its stable and unstable directional manifolds. Such unstable fixed point and its accompanying manifolds shift in response to changes in system-wide parameters so that a feedback providing algorithm was developed for movement of the fixed point and manifolds toward the desired plotted system state point in response to control or modification of a selected system-wide parameter. As an alternative to moving the fixed point in accordance with a system-wide parameter, the system state point itself may be altered and brought closer to the fixed point. The latter strategy was employed to control interbeat intervals of the pulsating activity in living tissue for cardiac arrhythmia stabilization purposes in accordance with real-time calculation with sufficient rapidity to implement corrective control, as disclosed in the aforementioned Spano et al. patent.

A significant characteristic of a neural system associated with brain tissue is the presence of brief aperiodic bursts of focal neuronal activity, referred to as interictal spikes. Such interictal spikes occur between epileptic seizures arising because of nervous system disorders. It is therefore an important object of the present invention to provide a procedure for manipulating chaotic activity, based on the aforementioned study of chaotic regimes, by intervention at irregular times determined from real time calculations involving data obtained by monitoring of brain tissue behavior.

SUMMARY OF THE INVENTION

In accordance with the present invention, a strategy was developed for treatment of epileptic foci in the neuronal network of living brain tissue by monitoring the timing of intervals between system characterizing events such as spontaneous bursts to identify a chaos regime therefrom, involving determination of an unstable fixed point of a system state and accompanying directional manifolds during a learning phase, followed by a chaos control phase during which a waiting time is determined by real-time calculation before delayed intervention is instituted. Such intervention is designed to reliably restore the neural system state to a desired system state represented by an unstable fixed point at the intersection of its stable and unstable directional manifolds plotted as a function of the interval between said monitored burst events. The intervention is delayed by the real-time calculated waiting time, based on switching of the chaotic regime to a periodic pacing condition according to natural system behavior. A minimal time period modifying type of intervention is utilized for reliable shift in system state point.

The aforesaid intervention waiting time is terminated by injection of a stimulus, into the brain tissue to cause corrective movement of the system state toward an unstable fixed point. If the next spontaneous burst corresponds to an interval point close to the unstable fixed point, intervention is suspended until the system state moves away from the unstable fixed point, at which time the behavior modification program is recycled.

In accordance with another embodiment of the invention, a behavior modification program when used to modify pulsating activity of brain tissue by application of stimulus intervention thereto through electrodes, employs an anti-control chaos strategy based on the recognition that the neural system is characterized by motion of points of spontaneous bursts along a stable manifold path toward the unstable fixed point of the chaotic regime and away from such unstable fixed point along an unstable manifold path by properly delayed stimulus intervention. The stimulus intervention, whether of the anti-control type or of the control strategy type involves injection of either single pulses or trains of pulses of electrical energy of different shapes.

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Obviously, other modifications and variations of the present invention may be possible in light of the foregoing teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.