Ph.D Thesis

Ph.D StudentOfek Einat
SubjectCharacterization of the Neural Response to Subjectively
Significant Verbal Stimuli Using Evoked
DepartmentDepartment of Medicine
Supervisors PROFESSOR EMERITUS Hillel Pratt
PROF. Shimon Marom
Full Thesis textFull thesis text - English Version


Neural correlates of emotions have been described assuming universal emotional valence of stimuli, without individual assessment of the subjective valence. Related brain activity has been typically traced with fMRI's (functional magnetic resonance imaging) temporal resolution of seconds. Previous studies of emotion analyzed mainly the direct effect of subjectively significant stimuli on brain activity.

    The purpose of the study was to characterize the brain response to subjectively significant stimuli, in 3 aspects:
  1. The direct brain response to subjectively significant stimuli.
  2. The time course of brain activity modulation by preceding subjectively significant stimuli.
  3. The autonomic response to subjectively significant stimuli.

Thus, electrical brain activity was recorded from 16 normal subjects, during 2 experiments and the autonomic responses were recorded in a third experiment. The stimuli chosen for all experiments were common Hebrew first names. The subjective significance of the stimuli was individually assessed for each subject after the 3 experiments, using a validated questionnaire.

A specific brain response to subjectively significant stimuli was found. Significant brain activity to subjectively significant stimuli began as early as 200 ms (milliseconds) after stimulus onset, with increased brain activity in the vicinity of several brain areas, including frontal gyri, Broca's area, Wernicke's area, insula, precuneus and cingulate gyri. The time course of activity in these areas was traced and found concurrent.

In the cued attention task, significant cue validity effects were found in the response to targets. Language related areas were mostly involved following neutral distracters. Emotionally activated areas were mostly involved following subjectively significant distracters. Thus, cue validity and subjectively significant distracter effects seem to have distinct effects.

A larger autonomic response was recorded to subjectively significant stimuli as compared to neutral ones.

The results of the study indicate a specific brain response to subjectively significant stimuli. It is possible to distinguish between the responses to different subjectively significant stimuli. There is interaction between cognitive and emotional processes. Brain response (event related potentials) was found to be a more accurate measure than the autonomic response.

Evoked potentials may be used as a measure for distinguishing emotionally-loaded stimuli.