What's truly extraordinary is not the structure but the patterns of connectivity that flow through it which underlie everything that makes you, you.
Level of Consciousness
What in the brain that determines whether we are conscious or not?
The intralaminar thalamic nuclei are part of the thalamus, which sits in the centre of the brain, at the top of the brainstem. If this part of the brain is damaged, it will shut off consciousness entirely.
The claustrum, a thin sheet of tissue deep inside the brain, also seems to have an important role in whether we are conscious, or awake but unconscious.
The claustrum acts as a kind of conductor of consciousness, which integrates information across distinct regions of the brain and binds together information arriving at different times.
Guilo Tononi says that for a system to be conscious, it must integrate information in such a way that the whole generates more information than the sum of its parts. According to Guilo Tononi, we lose consciousness when we go to sleep because this is the time when information from the brain's specialised circuits is no longer integrated. The reason why the brain seizures associated with a loss of consciousness is seizures overload the circuits, blocking complex informational exchange.
In terms of which brain regions are involved in maintaining conscious level, attention has recently been drawn to a posterior 'hot zone' in the cortex- centered on the parietal and occipital cortex. Activity in this area seems to distinguish very reliably between conscious and unconscious states.
The brain combines sensory information coming from the world, with its prior assumptions or expectations about the way the world is. This leads to a 'best guess' about what caused the sensory signals- and this is what we consciously perceive.
The content of our conscious perceptions is largely a construction of the brain: ' a controlled hallucination' in which our perceptual predictions are continually reined in by sensory signals impinging from the outside world.
Fronto-parietal network lights up when people report a conscious perception, compared to when they don't.
The brain actively selects which information to send to our eyes see the same scene, so the brain can easily combine the two monocular inputs into a coherent picture. But present the left eye with an image that's dramatically different from what the right eye is seeing , and experiments have revealed that the brain resolves this conflict by allowing you to see only one image at any one time. In other words, you are only conscious of either the left-eye image or the right-eye image , but never both simultaneously.
Our experience of reality is actually a kind of controlled hallucination generated by the brain.
Recent research suggests that conscious perception requires brain activity to hold steady for hundreds of milliseconds. The signature in the pattern of brainwaves can be used to distinguish between levels of impaired consciousness in people with brain injury.
Neuroscientists think that consciousness requires neurons to fire in such a way that they produce stable pattern of brain activity.
Types of Neurons
Von Economo Neurons
- allow the high-speed connections necessary for rapid emotional and intuitive judgements. These cells are found in just two small areas of the brain.
- have a important role in our sense of self
Motor Neurons
- send signals to parts of the body, eg muscle, to direct movement
Pyramidal Neurons
- involved in many areas of cognition-such as object recognition within the visual cortex
Inter Neurons
- bridge connectors between other neurons
Sensory Neurons
- transmit signals from the rest of the body to the brain
The Sense
Our experience of being an integrated self is also the brain's best guess at the causes of signals that arise from our bodies, the environment and our social world.
The self is constantly changing. Each time we recall an episode from our past, we remember the details slightly differently, and in doing so alter our personal history: a key aspect of the experience of being a self.
A conscious choice or inevitable?
When we have to make a decision based on visual input, for example, groups of neurons start accumulating visual evidence in favour of the various possible outcomes. A decision is triggered when
the evidence favouring one particular outcome becomes strong enough to tip its associated assembly of neurons across a threshold.
A Sense of Agency
One way the brain produces the experience of control is by adjusting when we perceive our actions, and their outcomes.
The source of our agency in the brain, two areas that seems to be particularly important are the anterior insula and the angular gyrus, which lies in the parietal cortex.
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