Study On P300 Potentials And Their Application Value In The Forensic Medicine

Cognitive process is a complex and sophisticated mentation,involving perception, attention, memory, thinking and other psychological activities.In forensic identification, orthodox CT and MRI can only provide limited information in morphology, and all kinds of Psychology Scale are vulnerable to subjective factors and education degree. Therefore, the study on the objective methods to evaluate cognitive function after brain injury have a great significance.When subjects identifying "target stimuli" of low probability in the stimulation sequence,The largest positive wave with eclipse period of 300ms recorded from scalp,called P300 potencials. P300 have the most closely relationship with cognitive function and widely used in ERP Intracerebral hematoma, cerebral contusion patients have a long P300 latency and decreased amplitude.Patients with mental disorders after brain injury also have similar results. But the research of the relationship between different parts of brain injury and P300 potentials is less, and the relationship between P300 and a variety of senior mentation is not clear.This study based on "active" and "passive" P300 testing in normal and brain injury patients, researching P300 waveform characteristics, and analyze the difference of P300 latency and amplitude in inormal and patients with different parts and vary degrees of brain damage,then finding objective basis on P300 in evaluating cognition disorder of brain injury patients.Subjects and methodsSubjects:20 normal subjects from China Medical University,pure tone air conduction hearing thresholds of different frequency were <25 dBHL. 30 patients with brain contusion, the frequency pure tone air conduction hearing thresholds were <25 dBHL. All patients had a clear history of head injury, brain contusion diagnostic were confirmed by CT and MRI with the checking time from 6 to 12 months after injury.Test Methodsxhecking in the silent cabinet,deploying international standards for upgrade methods to carry out pure tone test. Recording by NDI200 P+ electrophysiolograph, the platform period of 25 ms short pure tone in the spike, target stimuli frequency 2000 Hz,probability of 20%, non-target stimuli frequency 500 Hz,probability of 80%,sound intensity 72 dBHL.Band-pass filter set to 1～30 Hz,stimulating interval 1.1 / S, scan time 75 ms,build up 50 stacks. Recording electrode placed Cz, Pz, the reference electrode in the earlobe, the center of the forehead under 1 cm grounding electrode.Alone Electrode impedance<5kΩ,between electrode impedance<3kΩ.Results1. Normal and brain injury patients can be induced two positive and negative waves by target stimuli,eclipse periods between 70～500 ms,respectively N100,P200, N200 and P300.2. N200, P300 in"silent count" and "foot pedal" task state have a short latency and high amplitude than "passive" task state.3.There was no significant difference (P> 0.05)in P300 wave latency of Cz and Pz point. N100, P200 amplitude at Cz points higher than Pz, Pz P300 amplitude is slightly higher than Cz point.4. N200, P300 latency of brain injury patients have a reduced amplitude and long latency. N200, P300 latency of patients with diffuse cerebral contusion were significant differences (P <0.05) to the remaining groups.5.The changing of P300 lentency is obvious in the patients with attention disorder.Conclusion1.Types of tasks mainly effect N200, P300 amplitude. N200 and P300 latency in "Passive" site can be used as a measure of cognitive function.2. N200, P300 of patients with cerebral contusion have a long latency and decreased amplitude,"passive" P300 latency can be used as an objective methods in finding cognitive function in patients with diffuse brain injury.3. P300 latency is a comprehensive index reflecting attention, memory and the simple calculation of cognitive function, P300 latency is closely associated with attention.4. in the forensic identification, the "passive" P300 latency is a reflection of cognitive function in patients with brain contusion, can be used as an objective methods for detecting the patients with uncooperation..