Review: Conscious and unconscious emotional learning in the human amygdala

J.S.Morris, A.Ohman, R.J.Dolan, Nature, 393, 467-470

Reviewed by W. Williams

Different sides of the human amygdala are involved in emotional experience, depending on whether the emotional stimuli are perceived consciously or unconsciously.

Design:  A 2x2 factorial design exposed images of faces in pairs, to 4 groups of subjects. The second face was exposed for 45 ms, and masked the first, exposed for only 30ms. The first of the pairs were therefore perceived subliminally.

The experimental condition aversely  conditioned the subjects to the angry face through simultaneous exposure to white noise bursts, prior to the experiment. The control group were not aversely conditioned to the faces. Emotional awareness was tested through skin conductancy. 0% of the masked angry faces were detected, compared to 100% of the unmasked angry faces. Neural activity of the subjects was simultaneously measured using PET scans.

Fig 1: The four conditions.

mc=masked conditioned

nc=non-masked conditioned

mu=masked unconditioned

nu=non-masked unconditioned

To summarise: The experimental group saw two faces in quick succession, the second masking the first. Group 1 unconsciously perceived an aversely conditioned angry face, whereas group 2 were consciously aware of the aversely conditioned angry face.

Results:  The masked angry faces created a significant difference in neural activity in the right amygdala. The unmasked faces created significant activity in the left side. The active regions were specific to their experimental condition.

 

Fig 2: PET scans reveal

activity in the amygdala.

 

Left: Activity in the left

side the mc condition.

 

Right: Activity in the

right side, for the nc

condition.

Electrophysiological recordings of monkey amygdalas show the right side to be selective to faces and visually aversive cues.

Other functional imaging experiments have shown leftside responses to face perception processing (conscious).

Conclusions: The human amygdala can discriminate behavioural significance of stimuli without the need for conscious perception.

Processes involved in conscious awareness such as language may inhibit the unconscious processes of the right side.

Explains failure of previous experiments attempting to show involvement of amygdala, that used unmasked, consciously perceptible stimuli.

Future research: How might split brain patients react, verbally and emotionally, when perceiving these stimuli in either eye?