1. The split-brain phenomenon

2. background Remember that the corpus callosum, a huge set of axons, connects the two hemispheres Remember that the corpus callosum, a huge set of axons, connects the two hemispheres Also, severe epilepsy has caused its victims and the physicians dedicated to help them, to take drastic measures, including, on rare occasions, severing the corpus callosum Also, severe epilepsy has caused its victims and the physicians dedicated to help them, to take drastic measures, including, on rare occasions, severing the corpus callosum While the procedure slowed the epilepsy… While the procedure slowed the epilepsy…

3. Neurophysiology aspects 1. Each hemisphere controls the muscles on the other side of the body 1. Each hemisphere controls the muscles on the other side of the body 2. This curious fact even extends to how we see the world through our two retinas 2. This curious fact even extends to how we see the world through our two retinas 3. The left side of each retina sees the right side of the world and is then routed to the left hemisphere 3. The left side of each retina sees the right side of the world and is then routed to the left hemisphere

4. Neurophys cont. 4. The right side of each retina sees the left side of the world and then goes to the right hemisphere 4. The right side of each retina sees the left side of the world and then goes to the right hemisphere 5. For 95% of us, our left hemisphere controls our ability to speak, while our right is mute 5. For 95% of us, our left hemisphere controls our ability to speak, while our right is mute

5. More neurophys 6. For those of us who have an intact corpus callosum, fact #5 means little since our hemispheres easily communicate 6. For those of us who have an intact corpus callosum, fact #5 means little since our hemispheres easily communicate 7. But for those rare individuals whose corpus callosum has been severed …. 7. But for those rare individuals whose corpus callosum has been severed ….

6. Split-brain effect Without an intact corpus callosum, we could see an object ( a cat) to our left (with the image being sent to our right hemisphere) and not be able to tell someone what it was Without an intact corpus callosum, we could see an object ( a cat) to our left (with the image being sent to our right hemisphere) and not be able to tell someone what it was Our right hemisphere is always mute and now lacks any connection with the chatty left hemisphere Our right hemisphere is always mute and now lacks any connection with the chatty left hemisphere

7. Stranger yet …. But, amazingly, while the split-brain individual says, “I have no idea what that is”, he would be grasping a miniature cat in his left hand! But, amazingly, while the split-brain individual says, “I have no idea what that is”, he would be grasping a miniature cat in his left hand! Now, with two independent hemispheres, do we have two separate planes of consciousness? Now, with two independent hemispheres, do we have two separate planes of consciousness?