Transcript Slide 1

The brain, speech and language
pt 1
Yr 1 LCSC06
2015
Six layers of cells in the cortex:
Brodmann’s areas
C
Y
T
O
A
R
C
H
I
T
E
C
T
U
R
E
Hemispheric differences
Left hemisphere
typically contains
general interpretive and
speech centers and is
responsible for language
based skills
Right hemisphere is
typically responsible for
spatial relationships and
analyses
The right hemisphere and
communication
• Right hemisphere plays a role in pragmatics
• And prosody:
– Understanding the tone of voice, interpreting
emotion
– Using intonation to express emotions
• Face recognition
– prosopagnosia
Cortical areas and processing:
the role of association cortex
• Primary cortex:
• Deals exclusively with a particular function eg
vision, hearing, sensation, movement
• Ascending/descending tracts from spinal cord,
brain stem, special sense organs – originate or
terminate in the primary cortical areas.
• Higher order areas further process this
information
Unimodal association cortex:
• higher order integration of information
• extracts and processes information received and
puts it together with other info at a modality
level.
• Unimodal each of these areas deal with one
modality only ie sight, hearing, movement,
sensation
• this is to ensure that processing of sensory
information at this stage is not mixed up with
other sensory information
Association areas:
• Multimodal association cortex:
• highest level of information/cognitive
processing
• highest form of human thought occurs here.
• Information flows between these processing
sites
• So inter-modality processing: cognitive and
intellectual function, memory, learning, and
language
Association cortices involved in
language processing include:
•
•
•
•
•
The pre-frontal cortex
The perisylvian zone
Posterior parietal cortex
Lateral temporal cortex
Parahippocampal region
• Be sure you can locate these areas
Association cortex involved in planning /
initiation and sequencing of motor movements:
Revision: white matter pathways
• Association fibres transmit nerve impulses
between gyri in the same hemisphere
• Commisural fibres transmit impulses from the
gyri on one hemisphere to the corresponding
gyri in the opposite hemisphere
• Projection fibres form descending and
ascending tracts that transmit impulses from
the cerebrum and other parts of the brain to
the spinal cord or from spinal cord to the brain
Association White Matter Pathways
• Connect cerebral areas within each hemisphere.
• …and are generally bidirectional.
• Contain short association fibres known as "U" or
arcuate fibres that link adjacent cortical gyri.
• Long association fibres, all of which terminate in
the frontal lobe, include 5 types: the cingulate,
the arcuate fasciculus, the superior and the
inferior occipitofrontal fasciculi, and the uncinate
fasciculus.
Resources.med.fsu.edu
Conduction aphasia:
• Difficulty or inability to repeat, in the presence
of fairly fluent but paraphasic speech.
• Difficulty naming objects and cannot read
aloud accurately.
• May also have an impairment of voluntary
movement
Commissural White Matter Pathways
• Commissural white matter pathways connect
the 2 hemispheres.
• The largest is the corpus callosumCorpus
callosum has been described as the
‘information superhighway’ of the brain
• Ensures that each hemisphere ‘knows’ what
the other is doing
• Connected by myelinated fibres
www.cea1.com
Projection White Matter Pathways
• White matter projections consist of long tracts
that both ascend and descend.
• Projections that ascend are called corticopetal
tracts, while those that descend are called
corticofugal tracts.
• Names of specific projections include the
thalamo-cortical radiations, and the
corticospinal and corticobulbar tracts.
www.leonidzhukov.net
Occipital lobes
• Area 17 is the primary visual area.
• Areas 18 and 19 are the secondary visual
areas.
• Fusiform gyrus (Brodmann’s area 37) – part of
the visual association cortex. Possibly
responsible for visual letter/word form
recognition
• Damage results in letter-by-letter reading
Temporal lobes
Temporal lobes
• Virtually all the temporal cortex is involved in
language processing in one form or another
• The area known as Wernicke’s area (WA) is
not as clearly defined anatomically as Broca’s
area.
• WA found the superior margin of the temporal
lobe posterior to the primary auditory cortex
extending around the posterior margin of the
lateral fissure
Brain regions involved in language
processing
Auditory cortical areas
Auditory processing
• Auditory association cortex (adjacent to the
primary auditory cortex) is only activated by
speech sounds (and other human sounds such as
laughter, coughing) or writing (not other visual
symbols)
• The LEFT anterior auditory association cortex
distinguishes speech from other background
noise, writing from other visual symbols
• The LEFT posterior auditory association cortex is
activated during semantic tasks and retrieval of
words from semantic memory
• RIGHT anterior auditory association cortex is
activated by strong dynamic pitch variation (as
found in music and speech prosody)
• Middle temporal gyrus activated during
semantic processing, and possibly arranged in
a ‘semantotopic’ fashion
• Posterior inferior temporal gyrus anterior to
the cerebellum is concerned with visual
recognition or words and pictures, thereby
connecting the semantic areas with the visual
ones.
• Anterior inferior temporal area involved in
semantic decision making and may be
involved in analysing the phonemic content of
words.
Comprehension
• Can be for written or spoken language
• If former, visual input received at primary
visual cortex; if latter, primary auditory cortex
• Further processed by relevant adjacent higher
order and association cortices
• Same areas of cortex involved in linguistic
processing, no matter the modality of input ie
auditory or written, or output ie spoken or
written
Temporal planum
The insula
Broca’s area
Broca’s aphasia
• Results from damage to more extensive area
than the classical Broca’s area (BA)
• If confined to BA, pure apraxia of speech (AoS)
can result
• Anterior insula almost always involved
• As is the left frontal association cortex
• Right hemiparesis and right hemianopia is
common
Brain regions involved in language
processing
Thebrain.mcgill.ca
Supramarginal gyrus
• Involved in the phonological and articulatory
storage/processing of words ie motor plan
• And formulation of written language
The Angular gyrus
Angular gyrus
• Area of cortex above and below the upward
extension of the middle temporal gyrus
• Activated in complex semantic tasks such as
spoken and written sentence comprehension
• And in metaphorical thinking eg “It’s raining
cats and dogs”
Acquired dyslexia
• If due to small, circumscribed lesions at the
junction between temporal, parietal and
occipital lobes, can occur without disturbance
to speech/language
• Graphemic-phonological conversion affected
• Deep dyslexia has been reported when this
area is lesioned in dominant hemisphere
Transcortical aphasias
• Transcortical sensory aphasia results when
pathways between the association cortex and the
classical language areas are damaged. Lesions lie
in the tertiary association cortex around the
junction of the parietal, temporal and occipital
lobes, or inferior parts of left temporal lobe and
left thalamus
• Repetition is intact as BA and WA are still
functionally connected by the arcuate fasciculus
• Transcortical motor aphasia
• BA is disconnected from the SMA and other
areas of the frontal association cortex
• Non-fluent aphasia
• Preserved repetition
• May be a right-sided hemiparesis if
connections to adjacent motor areas are
involved
Subcortical structures with a role in
language
• Basal ganglia:
• Damage to the left caudate nucleus /putamen
results in a fluent aphasia with neologisms
• The thalamus:
• Different types of aphasia can result, with
anomia, poor comprehension, intact repetition
..and the cerebellum also has a role in regulating
behaviour and affect, due to connections with the
frontal lobes
Thalamus
• Key relay station between major sensory
inputs – vision, hearing , touch,
proprioception etc –and the cerebral cortex.
• Processes some info before passing it on.
• Receives input back from the cortex, allowing
some control over the stream of information
Normal direct/indirect loops of basal ganglia
Green = excitatory pathways, Red = inhibitory pathways
Premotor/motor cortex
(Glutamate)
Striatum
(GABA, ENK)
(GABA, SP)
External globus
pallidus
(GABA)
Subthalamic
nucleus
(glutamate)
Indirect
loop
Substantia
nigra
(dopamine)
Internal globus pallidus
(GABA)
Direct
loop
Thalamus
(glutamate)
Typical exam questions:
1)Describe the location and function of ‘mirror’
neurons
2) What is meant by ‘association cortex’? Name
one such area with relevance to language
processing.
3) On the diagram of the brain supplied, locate
the following: Heschl’s gyrus, the supramarginal
gyrus, Broca’s area, primary visual cortex