Event-related potentials as a tool in the diagnosis of affective disorders in children and adolescents

Emotional disorders are one of the most common psychological diagnoses in children and adolescents. It is known to be associated with major impairment in childhood and adverse consequences in later life. Epidemiological studies show that rates of depressive disorder in young people are higher (3-8%) and most severe to females than in children (1-3%) for both genders. Depression in children and adolescents has recently started to be studied with the use of objective methods. The current review article aims at presenting the latest findings in diagnosis, treatment and prognosis of the disorder using Event-Related Potentials (ERPs). ERPs provide an objective tool to investigate neural processing and have therefore been extensively used to study brain mechanisms of cognitive functions. Endogenous components of Event- Related Potentials provide sensitive measures to assess information processing. In particular, this article refers to all the basic ERPs waveforms (MMN, LDN, P300, P200, N100, N200 and CNV), and how those diversify when diagnosing emotional disorders and memory dysfunctions, as a result of depression. Generally, the P300 waveform of the Event- Related Potentials, which is the most studied ERP component, signifies the integrity of information processing functions of the brain. It constitutes a scalp recorded electroencephalographic response, which is generated by multiple limbic and neocortical brain areas. It is elicited by infrequent target stimuli and its latency (300 ms in normal population) indexes the time taken for activating these brain regions.

More specifically, in depressed children and adolescents the P300 waveform shows increased amplitude and prolonged latency. In a similar way, the P200 waveform has increased amplitude. The N100 and N200 appear with prolonged latency, the Contingent Negative Variation (CNV) waveform shows decreased amplitude in depressed patients. The CNV waveform records the expectancy or vigilance. In its traditional form requires the presentation of a cue or warning signal and subsequently of a target stimulus. During the interval between the two signals, CNV appears, terminating just after the second signal. Finally, the Mismatch Negativity (MMN) and the Late Discriminative Negativity (LDN) waveforms have reduced latency. These waveforms are evaluating the auditory sensory memory.

Moreover, we present the basic brain regions, which generate these waveforms and have to be examined in depressive patients. The most important are located in the bilateral lower temporal (hippocampus is also suggested) and prefrontal cortex volumes and especially the left prefrontal cortex. As a result of abnormality of the brain regions that was found in depressive adolescents, we can figure out that not only the mood is influenced but also the attention. That leads to a basic suggestion of why the children with depression often have low academic performance since their cognitive functions appear to be affected.

Furthermore, the findings of the diagnosis of depression are based on the similar neurochemical disorder that is presented to depressive population and can be proved with the use of ERPs. It is suggested that the main neurotransmitters that are responsible for the depressive sympomatology, such as serotonin, GABA and dopamine, are both responsible for the genesis of the basic waveforms of the ERPs, such as P200 and P300. The final aim of this article is to evaluate the treatment of depression when this incorporates the use of pharmacotherapy or psychotherapy as well as the combination of both. Because of this we have included studies that have been done in adolescents that have followed both ways of treatment. We, also, present the recorded changes of ERPs waveforms, as an objective way to proof the results. In conclusion, these results constitute the basis of a pilot study now in progress by the Laboratory of Neuropsycology at the University of Thessaly.

Key words: ERPs, P300, MMN, depression.