Who is that
talking? - Function and dysfunction of efference copy and corollary discharge
in healthy people and schizophrenic patients
Otolaryngology – Head
and Neck Surgery, UCSF,
The concept of efference copy and corollary discharge is an
attempt to explain the phenomenon that most of us recognize the outcome of
self-performed actions as such and not as the result of externally generated
stimuli. The planning of every motor act generates an efference copy, which is
used to calculate the sensory experience this motor act will evoke and prepare
the parts of the brain involved in the processing of sensory information for
the upcoming stimulation. Thus, self-generated stimuli are ‘expected’ and so
the neural response to these stimuli is attenuated compared to externally
generated sensory stimulation. This mechanism enables the brain to distinguish
‘self’ from ‘other’.
A dysfunction in this internal model has been hypothesized
by Frith and colleagues (e.g. Frith & Done, 1988; Frith, 1992) to underlie
the most prominent symptoms of schizophrenia: auditory hallucinations and delusions.
Frith and Done in 1988 put forward a hypothesis that hallucinations and
delusions might be caused by a lack of self-awareness or self-monitoring.
The results of a number of experiments are presented, which investigated function and dysfunction of the efference copy mechanism during the motor act of speaking using EEG and MEG on a healthy subject sample and a group with schizophrenia.