Transcript The brain and language 3 - University of St Mark & St John

The brain and language 3
Yr 1 LCSC06
2015
The limbic system
The limbic system
• One of the oldest parts of the cortex phylogenetically
• Marginal area of cortex surrounding the diencephalon
• Comprised of highly interconnected, but dispersed
structures:
• Hippocampus
• Hypothalamus – has connections with the autonomic NS
• Amygdala
• Cingulate cortex – has connections with neocortex (outer
layer of the cortex)
• Olfactory bulbs
• Mammillary bodies
• http://appsychtextbk.wikispaces.com/Limbic+System
Limbic system
• Relates the organism to its environment based
on current needs and the present situation,
and based on previous experience
• Involved in memory, attention, detection of
familiarity, behavioural inhibition and in the
detection and expression of basic emotional
responses
• The limbic system regulates the function of the
hypothalamus
Hypothalamus
• Lies beneath the thalamus
• Consists of a collection of nuclei
• Responsible for some of the basic functions
that keep us alive:
• Body temperature (via ANS), hunger, thirst,
body growth (via regulation of the endocrine
functions of the pituitary gland)
http://users.swing.be/sw104779/hypothalamus.htm
Hippocampus (=seahorse)
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Part of the medial aspect of temporal lobes
A crucial role in learning and memory
A famous case: HM (Henry Molaison)
Plays a role in navigation (cf London cabbies!)
London taxi driver's brains
• And declarative memory
Wikipedia.org
Amygdala (= almond)
• Implicated in the detection of fearful or
threatening stimuli
Cingulate cortex
Numerous connections to other parts of the
limbic system and cortex
Involved in emotional regulation, pain response,
attention/executive functions, learning and
memory; implicated in OCD, schizophrenia and
depression
Olfactory bulbs
• Lie under the frontal lobes
• olfactory sensors arise from the bulb
• The bulb projects via the olfactory tract to the
olfactory regions of the cortex, which form part
of an elaborate network of connections, involving
the thalamus, hippocampus, hypothalamus,
amygdala and orbito-frontal cortex
• Think of the link between smell and memory…
Mammillary bodies
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A group of nuclei
Project to the thalamus
Implicated in memory
Damage results in a type of amnesia ie
Wernicke-Korsakoff’s syndrome
• Short-term memory affected
Summary of functions of the limbic
system:
• Together, the structures of the limbic system play
a role in:
• Memory
• Attention
• Detection of familiarity
• Behavioural inhibition
• Basic emotional responses (fear, rage)
• summary of the limbic system there are many
other clips on you tube
An entertaining and in-depth look at
the Limbic system from Prof Sapolsky,
Stanford University
• http://www.youtube.com/watch?v=CAOnSbD
SaOw
Imaging the brain
Structural and functional imaging of
the brain
• Structural imaging:
– Different types of tissue have different physical properties
– These properties can be sued to create static maps of the skull
and contents
– Most common structural imaging are:
CT scan (computerized axial tomography) and MRI (magnetic
resonance imaging)
Main types used in medicine/NHS settings
• Functional imaging:
– Measures the activity of regions in response to task demands
– fMRI and PET scans are main ones used in studying speech &
language/cognitive abilities
– Used mainly for research
CT or CAT scan
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Computed Axial Tomography
A series of X rays
Taken in many different directions
Computer programme works out how much of an X ray
beam is absorbed in different types of tissue
• The denser the matter, the more radiation is absorbed
and the whiter the appearance on the scan
• Contrast dye can be injected to pick out vascular
structures/bleeds etc
• Takes 5-10 mins
www.lifescript.com
L mca stroke
CT scan: tumour
CT scan: haemorrhage
MRI
• Creates images of soft tissue
• Does not use radiation and so completely safe
• Much better spatial resolution (ie the gyri can be
visualised much more clearly that CT scan)
• Better discrimination between white and grey
matter
• But NOISY! And sensitive to movement in a way
that PET is not…
• what is an MRI
PET scanning
• the mind - PET scanning and language
fMRI
• Designed to measure moment-to-moment
changes in the brain
• These changes may be associated with cognitive
processing (such as language)
• Brain uses about 20% of body’s oxygen; doesn’t
store any glucose
• Therefore if an area of the brain increases
metabolic activity, there is an increase to blood
flow to that region
• fMRI measures (indirectly) increased O2
concentration in blood
fMRI images
fMRI
• what is an fMRI
• A short video on how MRI scanners work
• There are a number of these on You Tube
Transcranial magnetic stimulation
TMS
• TMS = transcranial magnetic stimulation: not
a neuroimaging technique, but can be used to
inhibit/stimulate areas of the cortex
• rTMS used in research studies to simulate
lesions in healthy subjects
• Used in treatment studies to inhibit or
stimulate areas of the cortex, and to
supplement ‘traditional’ therapy techniques
• Michael Mosley has TMS
Neuroplasticity
• What is another way of saying continuity
breeds connectivity?
• Briefly explain how the synapse adapts to
repeated stimulation, which results in greater
connectivity
Neuroplasticity
• Neuroplasticity = the brain’s capacity to
change at the cellular/network - the ‘micro
level’ (Kolb, 1995)
• Behavioural plasticity = the brain’s capacity to
change in response to environmental change
or change in the individual (the ‘macro level’)
• An important principle as this governs
change/recovery after brain damage eg stroke
• Mechanisms of neuroplasticity include
biochemical, physiological and structural
changes
• The consequences of these changes are
expressed in behavioural plasticity ie change
in the behaviour of an individual as a result of
learning
Neuroplasticity: 3 types
• Biochemical/physiologic = at the level of the
cell ie the synapse
• Structural = at the level of brain structure
itself
• And behavioural = changes in the function or
behaviour of the individual
• The changes occur primarily in the cortex
• There is a close inter-relationship between all
three forms of plasticity
A complex dynamic interaction:
Microlevel
plasticity
Results in
changes at the
microlevel
Changes in the
brain
Learning of new
behaviours/skills
Kolb (1995)
So….plasticity results from and induces behavioural change
Neuroplasticity and recovery
• Plasticity can be adaptive (eg efficient rerouting within the brain, allowing for the
learning of new behaviours or skills)
• …or maladaptive (resulting in persistence of
aphasia signs, hemiplegia, hemianopia etc)
Neuroplasticity and learning motor
skills
• http://www.youtube.com/watch?v=8Vo-rcVMgbI
• BEFORE WATCHING THE VIDEO:
• REVISE the cortical areas involved in motor
planning/programming and execution
• REVISE EXCITATION AND INHIBITION AT THE
SYNAPSE
Synaptic pruning
• What is it?
• Occurs when?
• Why does it happen?
At the physiological level, what
happens in recovery?
• Structural changes within the neurons themselves:
– Damaged neurons can generate new axons/ dendrites;
new synapses can be formed (regenerative sprouting)
– Cells that have not been damaged grow new synapses in
the area surrounding the dead tissue (collateral sprouting)
• Functional changes:
– Reactivation of previously inactive connections/synapses
– Damaged cells have a lower threshold of response
– Increased efficiency of neural transmission at any given
synapse
Plasticity and experience-driven
therapy: the holy grail
Neural
organisation
of the
therapy
activity
Activities in
therapy
Neural
organisation
of function
Mechanisms
of plasticity
A good revision task
• You ask a client to repeat the word ‘tea’
• From the client’s perspective, outline all the pathways,
nerves and structures (of the head and neck, respiratory,
CV, brain and nervous systems) involved in this task
– ie a very elaborated ‘speech chain’
• Produce a poster displaying these pathways and
processes
• Finally, consider all the links in this chain that can go
awry!
Useful resources
• McGill University neurology resources
• A summary of the brain and language,
including the role of the right hemisphere.
• NB note the use of Brodmann’s areas in the
discussion