What are we fairly sure about in regards to consciousness?
It only happens when the thalamus and cerebrum are in communication;
it seems to be associated with a positive signal 300 ms after an event (the P300);
it seems to be connected with working memory and the start of further stages of memory;
it seems to be connected to the focus of attention;
it is probably discontinuous (like frames of a movie);
it seems to be involved in communication of its contents to many parts of the brain;
gamma waves (about 40 a second), start in the thalamus and move front to back in the cortex, create synchrony in their path, and are essential for consciousness.
There are theories that put these observations together, such as the global workspace model. I am not convinced that these theories are complete because they appear to by-pass the importance of the thalamus. For years there has been a concentration on the cerebral cortex as if it was the “brain”.
Where is the model that puts the thalamus in the center of the action?
Let us assume for a while that the thalamus is the seat of consciousness. When we wake up a group of neurons in the brain stem “wake up” the thalamus, it “wakes up” the cortex and establishes the thalamo-cortical loops, then we are conscious. When we go to sleep the brain stem puts the thalamus “to sleep” and it puts the cortex “to sleep”. Signals from the thalamus control the activity of most regions of the cortex: the input from outside, activity levels, wave synchrony. Signals from the thalamus coordinate attention and the use of working memory – but, they also are the source of the cycle that produces a “frame” of consciousness and feeds it to the hippocampus to become part of a memory. The gathering of the contents of a frame of consciousness through synchrony or short-term memory in the hippocampus allows a certain type of global access to relevant information across the cortex.
Of course the cortex also affects the activity in the thalamus – this is a two way street. But it does seem to me that the thalamus drives the mechanics of consciousness. Something like attention probably is controlled by the cortical products of cognitive processes, acting through cortical executive processes which feed back to the thalamus to be implemented by its control of cortical activity. There would be all sorts of complex interactions like this where the control was in effect circular. But – the thalamus would be the time keeper and the trigger for each stage of the cycle that produces consciousness.
I cannot see a model of consciousness that ignores the thalamus as any more acceptable than one that ignores the cortex.