What happens to human information processing during anesthesia: the effect of a sub-anesthetic dose of S-Ketamine

For nearly two centuries, we use general anesthesia for routinely extinguishing
consciousness during surgery. Yet, we do not know how consciousness arises in
the brain and what information is still present when people are under
anesthesia. However, it has been shown that with anesthesia not all information
processing is disrupted, some activity remains. The question we want to answer
is how much information the remaining activity still contains. To answer this
question, we will manipulate the level of information processing in different
ways. We will use a sub-anesthetic dose of S-Ketamine, that is commonly used in
anesthesia and different behavioral task to manipulate information processing.
By comparing the neural responses (using fMRI) and behavior between different
manipulations it is possible to infer which part of the information processing
is affected and which is not.

In a fMRI experiment, will measure the changes in brain activity patterns and
in functional connectivity. We hypothesize that a subanesthetic dose of
S-Ketamine impairs the functional connectivity, especially the feedback
connections that are important for consciousness to arise. Furthermore, we
expect that S-Ketamine will not affect the decoding of brain activity patterns
in the specific object related brain areas. But that S-Ketamine will impair
decoding in other brain areas where the information was not integrated. To
manipulate the decoding further, the visibility of the stimuli will be reduced
with masking. We predict that masking will have similar effects as S-Ketamine,
no effects in the object related areas but reduced decoding possibilities in
other brain areas. The final part will look at the effects of S-Ketamine on
different manipulations of conscious perception, especially task that require
different levels of information processing and different stages of
consciousness (visual short-term memory task, a backward masking task, and a
motion induce blindness task).

This double blind placebo controlled within-subject trial contains two sessions
(placebo and S-Ketamine). The order of the sessions will be random.

Subjects participate in 2 sessions with 1 week in between the sessions. Before
the participants are enrolled in the study, they will be thoroughly screened by
a psychiatrist to minimize any risk associated with participation. Furthermore,
the subjects will be well informed and will practice the tasks before the
sessions.
A psychiatrist/anesthesiologist will be present throughout the experiment to
monitor the participant. The participants are asked not to eat and drink 1 h
prior to the study and to refrain from caffeine containing drinks for 3 hrs.
Heart Rate and Blood pressure will be measured. Furthermore, Visual analogues
scales will be used to assess the mood and state of the subjects. The given
dose of S-Ketamine is a low dose with minimal chance on side effects. In the
anesthesiology department there is a lot of experience with this type of
recordings and it is not regarded as burdening for the participants. We regard
this protocol as a reasonable load on this group of participants, with
negligible risks.