Selective attention II: Electrophysiologic mechanisms and dysfunctions

Author(s): Klipstein, S. B.

Journal/Book: Salud Ment. 1995; 18: Calz Mexico-Xochimilco #101, Mexico City 22 DF, Mexico. Inst Mex Psiquiatria. 49-56.

Abstract: In order for the central nervous system (CNS) to process the baggage of sensory information to which it is constantly exposed, a selection of information takes place. The brain processes that make this possible is called selective attention. In this second part we describe the main findings of the electrophysiology of selective attention as shown by electrical recording of potentials induced by sensory stimulation, as well as studies on the otoacustic response and on unitary activity recordings. Event-related potentials (ERPs) or evoked potentials provide a high temporal resolution and the non invasive requirement necessary in normal human studies. Various ERPs components associated with cognitive operations involved in selective attention have been identified. In the case of auditory selective attention, a negative potential, beginning at about 60 msec and peaking at approximately 100 msec (N100) after the signal onset, is generated in the primary auditory cortical area. This response has been called processing, or differential negativity. Other components of ERPs have shown changes associated with attention, including a late positive wave, called P300, and the contingent negative variation (CNV). The P300 shows a negative correlation between its amplitude and stimulus ocurrence probability. The CNV has been considered as a measure of expectancy. In an attempt to identify whether information selection occurs in the first relays of sensory pathways, as proposed by Hernandez-Peon in the ''central control of afferent activity'' hypothesis years ago, otoacustic responses have been studied. An otoacustic response is obtained by the recording of the sound emitted by the cochlear hair cells as an ''echo'' of the incoming stimuli. It has been found that this response is larger when the subject attends the stimulus, suggesting that selection of information may occur at the sensory receptor level. However, these studies must be confirmed. Other reports point to the reticular nucleus of the thalamus as a candidate for functioning as a selective filter of sensory information arriving to the cerebral cortex. This structure surrounds the thalamus and receives collaterals from all thalamic afferents to the cerebral cortex. When unitary activity has been used, the most frequent paradigm has involved visual stimulation. Thus, in frontal and parietal cortices, the striatum and the superior colliculus among other structures, neurons have been found whose frequency discharge is directly related to the detection of relevant stimuli. Finally, we analyze the most common attentional pathologies found in the clinic: hemi-neglect, attentional deficits in children, and absences of epileptic origin (non-convulsive generalized epilepsy, or petit mal). We will refer to the types of pathologies of some brain regions that have shown involvement and the suggested physiopathological mechanisms. We conclude by emphasizing the need for an interdisciplinary approach in the study of selective attention in particular and cognitive processes in general, from complementary methodologies: behavioral, electrophysiological, psychopharmacological and of functional imaging.

Note: Article SM Ortega, Univ Guadalajara, Unam, Calle Rayo 2611, Col Jardines Bosque, Guadalajara 44520, Jalisco, Mexico

Keyword(s): AUDITORY EVOKED-POTENTIALS; POSTERIOR PARIETAL CORTEX; LIGHT-SENSITIVE NEURONS; LEFT SPATIAL NEGLECT; DIRECTED ATTENTION; VISUAL-ATTENTION; BRAIN; MODULATION; NUCLEI

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