Cerebral evoked potentials and semantic categories
Introduction. Cerebral evoked potentials represent variations in the electrical activity of the nervous system, excited by a sensory stimulus and which are recorded on the surface. They may be classified as endogenous or exogenous. Amongst the late endogenous evoked potentials (EEP) we may emphasize N400 which seems to represent the linguistic management wave, particularly for semantics. Objective. To observe the EEP recorded throughout the process of carrying out a task involving sequential semantic categorization. Patients and methods. Nine healthy subjects carried out a task based on a paradigm of sequential reaction time (RT), similar to that designed by us in 1994. The data recorded were the RT and EEP at the level of the electrodes Fz, Cz and Pz in five lots of stimuli (in the first four lots the same list of words were repeated and in the fifth and final lot a different, new list appeared). Conclusions. It was seen that only N400 varied during the procedure. This variation was related to familiarity with the task. That is to say that the amplitude of N400 was reduced when the same words were repeated and increased when new words appeared for semantic classification. The reduction in parallel, although not significant for RT, allowed the reduction in N400 alone to be followed whilst the task was carried out. It may be the electrophysiological marker of the process of learning semantic categorization
Objetivo Observar los PEC recogidos a lo largo de la realización de una tarea de categorización semántica secuencial.
Pacientes y métodos Nueve sujetos sanos realizan este ejercicio basado en un paradigma de tiempo de reacción (TR) secuencial, semejante al diseñado por nosotros en 1994. Los datos que se recogen son los TR y los PEC a nivel de los electrodos Fz, Cz y Pz, en cinco bloques de estímulos (en los cuatro primeros bloques se repite la misma lista de palabras y en el quinto y último aparece otra nueva lista).
Conclusiones Se observa que sólo la N400 varía durante la realización de la tarea. Su variación se produce en función de la familiaridad del ejercicio, es decir, la amplitud de la N400 disminuye con la repetición de las mismas palabras y aumenta cuando aparecen nuevos términos para clasificar semánticamente. La disminución paralela de los TR, aunque no significativa, permite sólo seguir la disminución de la N400 a lo largo de dicha tarea. Podría constituir el marcador electrofisiológico del aprendizaje procedimental de la categorización semántica
