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Summary Chapter 4 - The Brain (detailed)
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This is a very detailed summary on Chapter 4 - The brain of the Consciousness book (S.Blackmore) Third Edition
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Neuroscience and the correlates of consciousnessEliminative materialists; eliminate mental properties like qualia: they claim that the mental
states we assume to exist actually do not.
- People disagree fundamentally on the role of the brain (but agree that brain is
relevant to consciousness)
A human brain:
Brainstem: medulla, pons and midbrain
- Role in controlling cardiac, respiratory and sexual functions and arousal levels
Reticular formation: pain desensitization pathways and activates regions of cortex in
transitions from sleep to waking
Cerebellum: behind midbrain:
- Function: motor control and links upwards to motor cortex and downwards which
provides feedback on body position and the effects of actions
Thalamus: relay areas for sensory inputs -- form crucial parts of complex loops to and from
the cortex which lies above and around it. These thalamocortical loops have been implicated
in consciousness
Hippocampus: essential for laying down long-term memories and forming cognitive maps;
the amyg- dala, with roles in rewards and emotions
hypothalamus, which regulates the autonomic system including blood pressure, heart rate,
and sexual arousal;
cingulate gyrus: which is involved in emotion, pain, and motivational responses
2 main types of neurons:
- Excitatory pyramidal cells
- Inhibitory neurons
Cortex is arranged in 6 layers - layer 1 outside
2 hemispheres- linked by white matter of the smaller anterior commissure and much larger
corpus callosum
occipital lobe: vision
parietal lobe: sensory association areas & somatosensory cortex & the dorsal stream
temporal lobes: auditory areas & memory functions & the ventral stream
frontal lobes: large in humans, forward planning and executive functions.
Single cell recording
Fine electrodes are inserted into living cells to record their electrical activity. This technique
is widely used in animal studies, and more rarely in humans.
Electroencephalogram (eeG)
the eeG uses electrodes on the scalp to measure changes in electrical potential arising from
the com- bined activity of many cells in the underlying area of the brain. The human eeG
was first described in 1929 by the German psychiatrist Hans Berger, who showed that the
resting alpha rhythm (8–12 cycles per second) is blocked by opening the eyes or doing
mental arithmetic. In the 1960s, com- puter averaging improved the study of event-re- late
potentials (eRPs), including evoked potentials in response to specific stimuli, readiness
potentials that build up gradually before a response is made, and potentials associated with
unexpected events. Although the eeG has poor spatial resolution, it is still a valuable
research tool because of its good temporal resolution.
X-ray Computed tomography (Ct)
, Developed in the early 1970s, Ct scans are computer-gen- erated images of tissue density,
produced by passing x-rays through the body at many different angles and measuring their
attenuation by different tissues. the same mathematical techniques for constructing the
images are used in newer forms of scanning.
Positron emission tomography (Pet)
This is a technique for imaging the distribution of radioactivity following administration of a
radioactive substance. In Pet, atoms that emit positrons are incorporated into glu- cose or
oxygen molecules, allowing brain metabolism and blood flow to be measured directly.
Radiation detectors are arrayed on the head in several rings, allowing several slices of the
brain to be studied simultaneously. Pet has good spatial resolution but very poor temporal
resolution, and the added disadvantage of having to use radiation.
Nuclear magnetic Resonance (mRI)
mRI measures the radio signals emitted by some atomic nuclei when placed in a magnetic
field and excited by radio frequency energy. the radiation emitted provides information about
the chemical environment of the nuclei. In the 1970s, the idea of using hydrogen atoms in
the body for imaging was developed into fmRI (functional mRI), which can provide extremely
detailed images of living brains. early methods required injections of a paramagnetic
substance, but in the 1990s totally non-invasive methods followed, including the use of BoLD
(blood oxygen level-dependent) contrast, which allows measurement of local brain
metabolism. fmRI measures neuronal activity only indirectly, depending on metabolic and
haemodynamic responses to neural activity, which limits its temporal resolution. For brain
scanning, the head has to be placed inside the scanner and kept very still. the results are
displayed using false colour to produce the familiar coloured images of the brain in action.
Although they may look like direct representa- tions of brain activity, the published images
have gone through many stages of processing and statistical analysis and must be
interpreted with care: the readings are subject to noise at every stage of the process; false
positives are extremely easy to generate when a set of ‘standard assumptions’ are not met –
so easy that a dead Arctic salmon can appear to be engaged in a perspective-taking task;
and basic variables like breathing may be serious confounds. There are now numerous
open-science initiatives for enhancing validity and reproducibility in fmRI research, but we
must bear in mind its limitations.
transcranial magnetic stimulation (tms)
In tms, or repetitive tms (rtms), a coil held over the brain generates a pulsed magnetic field
which stimulates neu- rons in a focused area by inducing small local currents. stimulating
motor areas induces involuntary movements, and if the precise area stimulated is located by
scanning, this allows motor cortex to be accurately mapped. simi- similarly, visual or speech
areas can be mapped because tms suppresses function in the area stimulated. tms can also
be used to induce particular experiences or altered states of consciousness (Chapter 13).
- method of evading the mystery (or tackling the ‘easy problems’) is to look for ‘the
neural correlates of consciousness’ (NCCs).
Correlations before cause
studying the NCCs: to measure some aspect of neural functioning & then correlate it with
reports of conscious experience
‘contrastive method’: comparing measurements of neural functioning when a given action
or perception is conscious with when it is not conscious
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