Surgery – Diagnostic testing – Detecting brain electric signal
Reexamination Certificate
2001-11-27
2004-05-25
Hindenburg, Max F. (Department: 3736)
Surgery
Diagnostic testing
Detecting brain electric signal
Reexamination Certificate
active
06741888
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and apparatus for estimating the degree of neuronal impairment in the brain cortex, which can be used for early estimation of a senile dementia disorder.
2. Description of the Related Art
With respect to senile dementia, it is statistically said that about 30% of nonagenarians are in dementia. This senile dementia is becoming a serious problem for the coming aging society.
Accordingly, such a dementia disorder should be preferably found as early as possible and treated before it results in a serious state. The judgment of the dementia disorder has been conventionally performed by various manual methods as follows:
(1) Hasegawa's Dementia Rating Scale (HDS)
The HDS method is devised for screening demented old people from normal aged ones. The HDS is composed of questions which the normal old or aged people without an intellectual disorder can relatively easily answer. This method can be normally performed in 5-10 minutes.
The questions include 11 items such as “memory and registration”, which are main items, “orientation”, “calculation”, and “general common sense”. Predetermined weighting are performed to the points, based on the rate of passing the question items, according to the difficulty.
Also, with revised evaluation items, the HDS is replaced with the Hasegawa's Dementia rating Scale Revised (HDS-R) in which the examination can be performed if the birthday of the person himself/herself is solely confirmed.
(2) National Mental Research Dementia Screening Test
This national mental research dementia screening test is a standardized simplified test for accurately screening old people suspected of being dementia from healthy old people.
Namely, it is a screening test which easily enables co-medical staffs led by health nurses to use, give marks, and screen the persons for the purpose of performing health activities in respective districts finding out persons suspected of being dementia at an early stage, and adequately advising and guiding them. Also, this screening test can be used for the screening at the time of epidemiology investigation.
(3) N Type Mental Function Examination
The N type mental function examination is an old people's mental function examination which aims to measure an intellectual function in wider range, by adding questions on concept formation, diagram duplication, space recognition, movement formation function, and the like to questions on memory, orientation, and calculation.
This test can be used for distinguishing whether aged change of the mental function is caused by normal aging or disordered dementia. However, this test mainly aims to be performed to the old people suspected of being demented. For this reason, the test is prepared so as to evaluate a dementia degree (level) at a wide range of 5 stages, that is, normal, boundary, slight dementia, moderate dementia, and severe dementia.
(4) Mental Status Questionnaire (MSQ)
This MSQ (Mental Status Questionnaire) has been developed for a large scale investigation of old people at homes in New York City in 1958. Since the investigation is for many people socially, physically, and mentally quite different from each other, the aim of the investigation is to be performed simply, objectively, and easily, and to provide a reliable index for a mental function disorder.
As for question items of the MSQ, most distinguishable ones have been selected from among the question items including an orientation, a memory, a calculation, general and personal information by a preparatory test for hundreds of people. One half of the question items are composed of those for testing the orientation, while the other half question items are composed of those for testing a general memory, so that the emphasis is laid on the orientation test.
(5) Mini-Mental State Examination (MMSE)
This MMSE has been developed in a short and standardized scale for a neurophysiological examination of inpatients as shown in FIG.
11
.
Other various action observation scales (observation method) have been proposed as follows:
(6) Ezawa's “Clinical Judgment Criteria of Senile Intelligence”;
(7) Functional Assessment Staging Test (FAST);
(8) Clinical Dementia Rating (CDR);
(9) GBS Scale;
(10) N Mental State Scale For Old People (NM Scale).
Among above-mentioned prior art dementia judgment methods, it is found that the MMSE is a method securing a fixed reliability since the smaller the MMSE score on the abscissa in
FIG. 1
becomes, the neuronal loss ratio N obtained from autopsy becomes larger, so that the mutual relationship is assured. However, since this method adopts a test form in which doctors always examine subjects (patients) in interviews, there have been problems as follows:
{circle around (1)} Since a questioner exists, the answer greatly depends on the special human relationship between the questioner and the subject, and is not always objectively and accurately obtained, resulting in variation of the judgment result.
{circle around (2)} While the subject is repeating the test, he or she may learn the examination contents, so that the objective judgment result can not be obtained.
{circle around (3)} The subject occasionally refuses to answer.
Thus, in the prior art diagnosis methods, an objective method for distinguishing an early-stage demented patient from a normal person has not been proposed. Furthermore, in order to use it for dementia screening, the diagnosis method must be performed in a short time, at a low cost, and treated easily. However, a practicable method which enables the diagnosis of the demented patient at an early stage has not yet been proposed by the prior art methods including the above-mentioned methods.
Also, the methods utilizing the above-mentioned SPECT, PET, and the like need extremely short-life radioisotope materials, a cyclotron is required as a part of this system, which results in a greatly high cost.
SUMMARY OF THE INVENTION
It is accordingly an object of the present invention to provide inexpensive method and apparatus for estimating the degree of neuronal impairment in the brain cortex, which enable an objective judgment of an early dementia disorder without men's intervention for the judgment.
It has been widely known that human thinking, recognition, recall of memory, pleasantness/unpleasantness, mental fatigue, stress, and the like depend on an electrical action of a number of neurons in the brain.
Namely, it has been thought that signal transmission in a brain is performed by transmission of active potential impulses on nerve axons, and that the contents of the signal are encoded to a frequency of the impulses. When the action potential impulse reaches an excitatory synapse, electric current flows out of the connected neuron, through tissues outside the neurons, and returns to the original cell body. Since the current flow closely resembles that of a single current dipole, the electrical action of an individual neuron can be replaced with a single equivalent current dipole.
If activated neurons concentrate on a relatively limited place, their electric activity can be approximated by one or more such equivalent current dipoles.
In order to find out such current dipoles, the potentials (or magnetic field strengths) which appear at the positions of EEG (MEG) sensors on a scalp at the time when one or more current dipoles having an arbitrary moment are arbitrarily placed in the head are calculated, and the mean squared value of the errors between the calculated potentials and the potentials (or magnetic fields) measured by the sensors is calculated.
The current dipoles are moved until the position, the direction, and the value where the mean value of the squared errors becomes least are obtained, which is made an equivalent dipole.
If non-uniformity occurs in the neuronal activity in the cortex as a result of Alzheimer's disease, this non-uniformity appears in the scalp potential. Since the scalp potential distribution is smooth, deviations from this smooth potential give
Asada Takashi
Musha Toshimitsu
Brain Functions Laboratory, Inc.
Hindenburg Max F.
Staas & Halsey , LLP
Szmal Brian
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