In this section an overview on evoked brain potentials will be introduced, same as the bases of electrophysiology of the brain. The main research findings on evoked potentials and other psychological variables such as cognition, emotion, motivation and personality will be presented. The emphasis will be given to the relationship between evoked brain potentials and personality operationalized by previously presented two personality theories: Eysenck's and Strelau's theory. Even though it is possible to expect, based on arousal theory, that introverts who had higher sensory reactivity on physical stimuli of moderate intensity and higher levels of cortical arousal than extraverts, would also show higher P300-amplitudes in both modalities, audio and visual, due to other significant variables (i.e. task type, other psychological and physiological characteristics of subjects, etc.) some other results could be expected. Therefore, all complexity about the relationship between evoked brain potentials and human personality and relevant research methodology will be presented here.
TopEvoked Brain Potentials
The first application of electroencephalogram in examining brain-behavior relationships is related to the year 1929, when the Austrian psychiatrist Hans Berger published the first scientific paper in which he described in detail and interpreted the results of 73 recordings of the electrical activity of the brain of his ten-year-old son Klaus (according to Gloor, 1969). Since then, a series of electro-cortical studies have been made considering the relationship of the EEG (spontaneous electrical changes in the brain) with a series of psychological variables (Hugdahl, 1995b) with more or less success, due to the difficulty in controlling the impulses (Gale, 1987). Several decades later, in the early 1960s, due to the growing demand and interest for systematic electrophysiological studies of individual differences, and the technical improvements of the existing methodology (attempts to eliminate defects of EEG methods), there has been a method application expansion of evoked potentials of the cerebral cortex (Stelmack & Houlihan, 1995).
“Evoked potential is a by-product of electrical activity in the peripheral and central nervous pathways, which occurs as a response to external stimulation” (Dabić-Jeftić & Mikula, 1994a, p.8). The name evoked potential is because these resources, during the electroencephalogram recordings, are caused by certain stimulation (Polich, 1993), which represents the response of the human brain, which is the time related with given stimuli (Hugdahl, 1995b). It is the voltage change in EEG activity that is time related to sensory, motor or cognitive events. The basic difference between evoked potentials and spontaneous EEG waves is that the first appear in a specific time compared to the given stimuli, usually only in one part of the cerebral cortex. They can be used to identify and classify perceptual, memory, and linguistic operations, and in general at the time and classification labelling of specific phases in the information processing. Evoked brain potentials arise from the synchronous activity of a large number of neurons that are active in a given moment during the information processing. The parameters of evoked brain potentials, amplitudes, and latencies are obtained from the so-called signal averaging of summarizing process of time related electro cortical responses that occur at each reset the stimulation. Thereby, evoked potentials and EEG waves are separately summed, causing a gradual reduction in the amplitude of EEG noise and extraction of evoked brain activity that is otherwise difficult to distinguish from the background of EEG activity. They can be captured for each sensory modality under specific recording conditions of evoked potentials. The characteristic waveforms correspond to each modality. Components or peaks in evoked potentials usually have names of positive or negative waves depending on their polarity and latency. Their latency is typically shown in milliseconds: the earlier appearance of specific component is more likely to be determined by the physical properties of stimuli.
There are two groups of evoked brain potentials: evoked (already mentioned, which are following the physical stimuli from the environment) and emitted (those associated with processes such as preparing for cognitive or motor activity or observation of new, unusual stimuli in the environment) brain potentials (Picton, 1980), as they were defined by the original authors (Sutton, Brar, Zubin & John, 1965). Looking at the context in which the stimuli occurs (Brinar Brzović, Vukadin & Zurak, 1996), evoked (sensory or exogenous) resources, represent the brain's response to a specific sensory stimuli and event-related potentials (cognitive or endogenous) represent voltage fluctuations related to the time with some physical or psychological event, although they are not closely related to it, and can be skipped if a person is not interested in this stimulus. Sensory-evoked potentials or the so-called early components occur within the first 100 milliseconds after of stimuli and have very low amplitudes (0.1 - 20 μV). Event-related potentials or late components have a long latency (longer than 100 milliseconds) and larger amplitudes depending on the context in which the stimuli occur. Described EP-waves are shown in Figure 1.