HNS46, HNS47 Higher Cortical Function I and II Flashcards
***Development of vertebrate brain
3 Primary Vesicles —> 5 Secondary Vesicles
Prosencephalon (forebrain)
—> Telencephalon —> Cerebral hemisphere (+ Lateral ventricle)
—> Diencephalon —> Thalamus (+ 3rd ventricle)
Mesencephalon (midbrain) —> Mesencephalon —> Midbrain (+ Aqueduct)
Rhombencephalon (hindbrain)
—> Metencephalon —> Pons + Cerebellum (+ Upper 4th ventricle)
—> Myelencephalon —> Medulla (+ Lower 4th ventricle)
記:
Pros —> Mes —> Rhomb
Tel —> Di —> Mes —> Met —> Myel
Cerebral hemisphere —> Thalamus —> Midbrain —> Pons + Cerebellum —> Medulla
Cerebral cortex
Evolutionarily newest part of Cerebral cortex —> “Neo” cortex
Controls nearly all aspects of behaviour, including perception, language, decision making
6 layers (usually no neurons in 1st layer)
Coronal section of cerebrum
- Caudate nucleus
- Putamen
- Globus pallidus
- Lateral ventricle
- Cingulate gyrus
- Amygdala
- Insula
- Operculum
4 Lobes of Cerebral hemisphere
- Frontal lobe
- Prefrontal cortex
- Premotor cortex
- Primary motor cortex - Parietal lobe
- Primary somatosensory cortex
- Sensory association area - Temporal lobe
- Primary auditory cortex
- Auditory association cortex - Occipital lobe
- Primary visual cortex
- Visual association area
Divided by 3 sulci:
- Central sulcus
- Lateral sulcus (Sylvian fissure)
- Parietal-occipital sulcus
Functions of cerebral lobes
- Frontal lobe
- emotions, personality, social control, speaking
- executive functions e.g. planning, attention, decision making (PFC)
- control of movement (Premotor cortex + Primary motor)
- speech (Broca’s area) - Parietal lobe
- anterior part: somatosensory function (Primary somatosensory cortex)
- interpretation of shape / textures
- understanding speech and formulating words (Wernicke’s area) - Temporal lobe
- Hearing (Auditory cortex)
- storage of auditory experience
- memory storage —> ∵ Hippocampus wrapped inside temporal lobe - Occipital lobe
- visual information processing
- correlate visual images from previous visual experience
Gyrus vs Sulcus
Gyrus: Ridge on cerebral cortex
Sulcus: Depression / Groove in cerebral cortex
***Neurons in cerebral cortex
Most abundant type: ***Excitatory pyramidal neurons (cell body: pyramidal shape)
Other excitatory: Stellate neurons
Inhibitory: Interneurons
Pyramidal neurons:
- ***Spiny neurons (projections from dendrite —> dendritic spine —> postsynaptic membrane of excitatory synapse)
- Apical + Basal dendrites
- ***Excitatory (Glutamatergic)
- Glutamate, Aspartate
- ***Homogeneous morphology
- 70-80%
Interneurons:
- ***Non-spiny
- ***Inhibitory (GABAergic)
- GABA (γ-aminobutyric acid)
- ***Heterogeneous morphology
- 20-30%
Laminar organisation of cerebral cortex (6 layers)
- Composed of Glial cells + Neurons
- Gray matter
- Different inputs / outputs of different layers (e.g. Thalamic input: layer 4, output to Thalamus: layer 6)
—> Different functional units - 6 layer (based on morphology) (X rmb):
1. Molecular / Plexiform
2. External (Outer) granular
3. External pyramidal
4. Internal (Inner) granular
5. Internal pyramidal
6. Multiform (Polymorphic)
Brodmann’s areas
Based on histology —> 52 regions
Columnar organisation of cerebral cortex
Columnar function organisation —> a “column” of cells with:
- ***Similar response properties
- Overlapping / Nearly ***identical receptive field
Example:
- Visual cortex
- Ocular dominance columns (Binocular vision / Depth perception)
- Orientation columns (detect Orientation) - Auditory cortex
- Binaural bands
- Iso-frequency bands
Thalamocortical projections / relationships
Example:
- Anterior nucleus (from hippocampus / mammillary bodies) —> ***Cingulate gyrus
- Medial dorsal nucleus (from amygdala / olfactory bulb) —> **Prefrontal cortex + **Limbic system
- VPL (from Spinothalamic tract / Dorsal column-Medial lemniscus tract) —> Primary somatosensory cortex (Postcentral gyrus)
- Lateral Geniculate nucleus (from retina) —> Primary visual cortex
- Medial Geniculate nucleus (from cochlea) —> Primary auditory cortex
4 ***Functional categories of cerebral cortex
- Primary motor
- Primary sensory
- Primary sensory areas (***except olfactory) receive thalamocortical fibres from diencephalic (Thalamus) relay nuclei related to their functional modality - Unimodal association cortex (Secondary)
- Premotor area / Supplementary motor cortex: preparation, organising, planning sequence of movement - Multimodal association cortex (Tertiary)
- **Temporal association cortex
- **Parahippocampal cortex
- ***Cingulate cortex
Unimodal association area / Multimodal association area
Unimodal association area:
- ***Adjacent to primary cortex
- Devoted to ***higher level of information processing
Multimodal association area: - Receive information from several ***different sensory modalities —> production of a ***unified perception —> representation of perception in ***memory —> ***cognitive functions: 1. Use of language 2. Future planning 3. Imagine and create 4. Appreciation of space etc.
Motor areas - Control voluntary movement
- Primary motor cortex (Area 4)
- Premotor cortex (Area 6)
- Frontal eye field (Area 8) (visual attention, voluntary saccade, pursuit eye movement)
- Broca’s area (Area 44, 45) (language)
Primary motor cortex
- Location: Precentral gyrus
- Conscious control of precise, skilled, voluntary movements (on opposite side of body)
- Represented in orderly manner in cortex
- Body mapped upside down (Lateral: Face + Upper limb; Medial: Lower limb)
- Body regions with greatest number of motor innervation —> Largest areas of motor cortex (e.g. face, fingers)
- Disproportionate representation of body on primary motor cortex
Voluntary movement
- Mediated by direct connections
—> Cortex —> Internal capsule —> Spinal cord —> Corticospinal tract - Continuous stream of tactile, visual, proprioceptive information needed
—> from **Basal ganglia, **Cerebellum
—> Accurate + Properly sequenced voluntary movement
Sensory areas - Conscious awareness of sensation
- Primary somatosensory cortex (Area 1, 2, 3)
- Visual cortex (Area 17)
- Auditory cortex (Area 41, 42)
- Vestibular cortex
- Gustatory cortex (Area 43)
- Olfactory cortex
Primary somatosensory cortex
- Location: Postcentral gyrus
- Receives information from skin + skeletal muscle —> VPL, VPM of Thalamus
- Body regions with highest densities of receptors —> Largest areas of sensory cortex
- ***Exhibits spatial discrimination
—> column receive inputs from same body area with a specific sensory submodality (rapidly adapting (e.g. vibration) / slowly adapting (mechanoceptive))
Homunculi of human body
Disproportionate number of neurons of body on Somatosensory + Motor cortex
—> Disproportionate representation of body
—> Magnification of hands, lips, tongues
Primary visual cortex + pathways
Image of entire visual field —> Upside-down + Laterally reversed on retina
- ***Retinotopic (pattern recognition + feature extraction)
Visual pathway:
Photoreceptor cells —> Bipolar cells —> Retinal ganglion cells
—> Optic nerve —> Optic chiasm —> Optic tract
—> LGN of Thalamus
—> Optical radiation
—> Visual cortex
***Rmb:
左右
- Nasal / Medial visual field —> Optic chiasm —> Contralateral Lateral Geniculate nucleus —> Contralateral visual cortex
- Temporal / Lateral visual field —> Ipsilateral Lateral Geniculate nucleus —> Ipsilateral visual cortex
(Left visual field —> Right visual cortex)
上下
- Upper visual field —> Lower retina field —> **Lateral LGN —> **Temporal / Inferior optic radiation —> Inferior visual cortex
- Lower visual field —> Upper retina field —> **Medial LGN —> **Parietal / Superior optic radiation —> Superior visual cortex
(Visual cortex divided into Superior / Inferior by Calcarine fissure)
正中 (Macula)
- Central visual field —> Central retina field —> **Central LGN (both sides) —> **Caudal visual cortex
Optical radiation
Divided according to location of fibres:
1. Temporal optic radiation (Meyer’s loop)
- process ***Superior visual field
—> Inferior visual cortex
- Parietal optic radiation (Superior trajectory)
- process ***inferior visual field
—> Superior visual cortex
6 layers of LGN
6 layers of LGN —> Different types of cells —> Different columns of visual cortex
—> Facilitate Ocular dominance columns
***Typical visual field defects + corresponding lesion site
- Optic nerve lesion (e.g. optic neuritis) —> Monoacular amaurosis (得一邊視力)
- ***Optic chiasma lesion (e.g. pituitary macroadenoma) —> Bitemporal hemianopia (失去左右外側視力)
- Optic tract lesion (e.g. cranial-pharyngioma) —> Homonymous hemianopia (失去right / left visual field)
- Temporal optic radiation lesion (e.g. post-temporal lobectomy) —> Homonymous upper quadrantic hemianopia (失去right / left upper visual field)
- Parietal optic radiation lesion (e.g. parietal glioma) —> Homonymous lower quadrantic hemianopia (失去right / left lower visual field)
- Visual cortical lesion (e.g. occipital lobe infarct) —> Dense Homonymous hemianopia with macular sparing (Similar to optic tract lesion but spared macular image) (得一邊視力但macular image spared)
Primary auditory cortex + pathway
- Area 41, 42 (deep in lateral sulcus)
- ***Tonotopic map (maintained throughout pathway to cortex i.e. all nuclei are tonotopically organised)
- Cochlear projections: ***Bilateral
Pathway Cochlea —> Cochlea nerve —> ***Spiral ganglion —> ***Cochlea nucleus —> ***Superior olivary nucleus —> ***Lateral lemniscus —> ***Inferior colliculus (brainstem) —> ***MGB (Thalamus) —> Primary auditory cortex
Vestibular cortex
Vestibular nuclei (Superior, Inferior, Lateral, Medial) —> Vestibular information processed in different parts of cortex (∵ massive balancing information to process) —> Subjective orientation + Integration of somatosensory + Labyrinth information
(X rmb
- Premotor cortex FEF
- Posterior Insula + Temporoparietal cortex (PIVC)
- Posterior parietal cortex)
Gustatory cortex + pathway
- Area 43
- deep within Insula + Frontal Operculum
Taste buds (from anterior 2/3 tongue, posterior 1/3 tongue, epiglottis)
—> CN7, CN9, CN10
—> **Geniculate ganglion + **Inferior Glossopharyngeal ganglion
—> ***Solitary nucleus (Medulla)
—> Central tegmental tract
—> Thalamus
—> Gustatory cortex
Olfactory cortex + pathway
Olfactory mucosa
—> Olfactory bulb
—> Olfactory cortex (different parts of cortex e.g. Anterior olfactory nucleus, Olfactory tubercle etc.
—> Hypothalamus / Amygdala / Hippocampus etc. (feeding behaviour, odour discrimination, identification)
***Association areas
- Areas not involved in primary sensory / motor function
- ***Higher cognitive function (e.g. learning, memory)
- ***Integrate diverse information
- Increase size of association cortex —> complexity of behaviour + mental functions
- Parietal association cortex
- **sensory guidance of motor behaviour (Visually-guided grasping)
- **spatial awareness
- ***selective attention - Temporal association cortex
- **recognition of sensory stimuli
- storage of **semantic (factual) knowledge - Frontal (prefrontal) association cortex
- organising behaviour
- **working memory
- **personality - Limbic association cortex (anterior ventral portion of temporal lobe)
- **emotion and **episodic (autobiographical) memory
Example: Sensory information processing
一路散出去:
Primary sensory area
—> Unimodal association areas
- Primary motor cortex + Sensory association area
- then —> Premotor cortex + Higher-order somatosensory association area
—> completed in Multimodal association areas (information from different sensory systems converges in multiple areas)
- ***Temporal association cortex
- ***Parahippocampal cortex
- ***Cingulate cortex
Example: Visual information processing
2 major parallel pathways terminate in different higher order areas of cortex
Ventral pathway (Form information):
- colour, shape, texture
—> Temporal association cortex
Dorsal pathway (Spatial information):
- position, motion, speed
—> Parietal association cortex
***Prefrontal cortex (PFC)
Functions:
- Higher ***cognitive function, planning
- ***Personality expression
- ***Decision making, working memory
- ***Social behaviour
Definition:
- Projection zone of ***Mediodorsal (MD) nucleus (Thalamus)
- Part of frontal cortex in which electrical stimulation does **NOT evoke movements (i.e. only part of frontal cortex **not related to motor)
Highly interconnected with other cortical, subcortical area, brainstem
Dysfunction / Abnormality —> Psychiatry disorders e.g. Depression, Schizophrenia
Lateralisation of cortical functions
Corpus callosotomy:
Surgical procedure for epilepsy —> remove corpus callosum (critical to inter-hemispheric spread of epileptic activity)
Demonstrated by Split brain experiment
Cerebral dominance: Language (左腦)
Speech area normally located in ***Left hemisphere
Wernicke’s area (Area 22):
- Sensory / Receptive speech
- ***Comprehension of written and spoken language + Formation of coherent speech
Broca’s area (Area 44, 45):
- Motor / Expressive speech
- ***Motor programs of speech + writing
See a word on screen
—> Visual cortex
—> Wernicke’s area (information concerning the word is interpreted)
—> ***Arcuate fasciculus
—> Broca’s area
—> Primary motor area (speak out the word)
***Aphasia
Absent / Defective speech or language comprehension
- Wernicke (Receptive) aphasia (諗唔到但係咁講野)
- unable to name objects
- unable to understand meaning of words
- articulate speech readily, but usually nonsensically - Broca (Expressive) aphasia (諗到講唔到)
- seldom speak spontaneously
- understand language perfectly
- maybe able to write perfectly - Global aphasia
- larger lesions in central region around lateral sulcus (initial stages of large left middle cerebral artery injuries)
- almost total reduction of ALL aspects of spoken + written language - Conduction aphasia
- interruption of Arcuate fasciculus
- comprehension is normal, expression is fluent
- difficulty translating what someone said to him into appropriate reply
Cerebral dominance: Space + Attention (右腦)
**Right parietal association cortex:
- most highly lateralised
—> **Spatial relationships
—> Related selective attention
—> Sensory guidance of motor behaviour (Visually-guided grasping)
Damage to right parietal association cortex (non-dominant cortex):
***Contralateral neglect
- Deficit in attention
- Deficit in spatial surrounding
—> Deficit in self-image on left side of body / deficit in perceiving world on left side
E.g. NOT wash / dress left side of body - Personal neglect syndrome
***Apraxia: Constructional Apraxia (not related to cerebral dominance)
(記: **Motor planning + **Spatial relationship + ***Sensory guidance of motor behaviour (Visually-guided grasping))
Apraxia: Disorder of motor planning
Constructional Apraxia:
—> NOT related to visual acuity / fine motor control
—> Difficulty with ***motor planning to perform tasks / movements
- Damage of **Parietal association cortex, **Premotor cortex, ***Supplementary motor cortex
- Inability to internalise + duplicate ***Spatial relationships of the individuals parts of the model
***Agnosia (not related to cerebral dominance)
- Inability to ***process sensory information
- “Not knowing”
- Describe a large group of higher level disorders of sensory ***perception even though afferent sensory pathways are normal
Example:
- Tactile agnosia (unable to recognise objects through touch)
- Prosopagnosia (inability to recognise familiar faces / learn new faces)
- Visual appreciative agnosia (inability to see object parts as a whole —> unable to construct sensory representations of visual stimuli even though can name them 明白但不能照抄)
- Visual associative agnosia (can create sensory representation normally but cannot associate with meaning能夠照抄但不明白意思)
***Ataxia (not related to cerebral dominance)
Lack of voluntary coordination of muscle movements
—> **gait abnormality, **speech changes, abnormalities in ***eye movements
Optic ataxia:
- Damage to ***Dorsomedial Parietal cortex
- Difficulty with ***visually guided grasping / reaching
e. g. Fail to shape their hand, orientate the hand / wrong location to grasp an object
Dementia
- Impaired **Cognitive function in **multiple domains but preserved consciousness
—> Deterioration of memory, intellect, concentration, comprehension, specific cortical functions (aphasia, agnosia, acalculia, visual-spatial disturbance) - Other features (***Motor):
—> abnormal movements, seizures, pyramidal / extrapyramidal signs, cerebellar ataxia, gait disturbance, primitive reflexes
Screening test: Mini-mental state examination —> test higher mental function examination: 1. Memory 2. Language 3. Visual-spatial orientation 4. Mathematical skills 5. Problem-solving ability 6. Personal / Social conduct
Causes: 1. ***Neurodegenerative diseases (e.g. Alzheimer’s) 2. ***Vascular dementia (e.g. infarct) 3. Metabolic disorder Etc.
***Alzheimer’s disease
- Most common form of dementia
- Familial (5-10%): Mutation of **amyloid precursor protein (APP), **presenilin 1 (PS1), ***presenilin 2 (PS2)
- Sporadic (90%)
- Chronic and progressive loss of neurons / synapses in cerebral cortex + subcortical regions (e.g. Hippocampus)
—> Memory loss, Deficits of cognitive function, Mood disorder - Neuropathology hallmarks
1. Extracellular deposition of **amyloid plaques, composed of **β-amyloid
2. Intracellular **neurofibrillary tangles (NFT), composed of **Tau: aggregates of highly phosphorylated microtubule-binding protein
3. Significant decrease in ***ACh transferase (synthesis of ACh) and loss of cholinergic neurons - Disease progression:
Medial temporal lobe (Poor memory)
—> Lateral temporal + Parietal lobe (Poor recognition)
—> Frontal lobe (Poor judgement, Short attention)
—> Occipital lobe (Visual problem)
Functional imaging of cognition
Energy metabolism of neurons —> influenced by changes in synaptic activity / synaptic strength
Shifts in metabolism are associated with local:
- ↑ Cerebral blood flow
- ↑ Cerebral blood volume
- ↑ Glucose uptake
- ↓ Deoxyhaemoglobin content
Detected by different techniques e.g fMRI, PET
Positron Emission Tomography (PET)
Detects pairs of **Gamma rays
- emitted indirectly by a positron-emitting **radionuclide (tracer) introduced into body on a biologically active molecule (e.g. glucose, oxygen-15, glutamate, GABA)
Example:
- Measures flow of blood to different parts of brain by ***oxygen-15
- PET scanning with tracer fluorine-18 fluorodeoxyglucose (FDG): FDG-PET
Advantages:
- Has ***specific targets (e.g. glucose)
- ***Fast temporal resolution
Disadvantage:
- Poor spatial resolution
- Radioactive
Functional Magnetic resonance imaging (fMRI)
- Measures brain activity by detecting changes in ***blood-oxygen level / blood flow
- Primary form: Blood-oxygen-level dependent (BOLD) contrast
Advantages:
- Not require to undergo shots, surgery, ingestion
- No radiation
- ***Better spatial resolution compared to PET
Disadvantages:
- Tiny movement can obscure and ruin fMRI data (do not affected PET)
- Poor temporal resolution
- No metal implants in body
Electroencephalogram (EEG)
- Non-invasive method to monitor electrical activity of brain
- Measure ***Electrical potential difference (result of summation of postsynaptic potentials from pyramidal neurons in cortex)
- Multiple electrodes on scalp
- Indication: Diagnose **epilepsy, coma, brain death, monitor **sleep stages
(Epilepsy: Chronic disorder involving an abnormality of electric activity of brain with/without apparent changes in nervous tissues)
Principle:
- **Local currents produced when neurons activated
—> currents flow through dendrites of many pyramidal neurons in cerebral cortex
—> generate potential differences
—> create **dipoles between soma and apical dendrites
—> ***summation of many neuronal activity
—> EEG
EEG patterns
Different frequency and different amplitude
—> Different waveforms
—> Alpha (8-13Hz), Beta (>13Hz), Theta (4-7Hz), Delta (<4Hz)
Alpha:
- person is **awake, **relaxed state of wakefulness
- eyes closed
- relatively regular, rhythmic, low-amplitude, synchronous waves
Beta:
- person is **awake, **alert
- produced by visual stimuli, mental activity
- rhythmic but less regular than alpha waves and with higher frequency
Theta:
- ***irregular
- common in children
- uncommon in awake adults but may appear when concentrating and under emotional stress
- occur in many ***disorders of brain
Delta:
- common during ***sleep and awake infant
- in awake adults —> indicate ***brain damage
- ***high-amplitude waves
Magnetoencephalography (MEG)
- Mixture of EEG and MRI
- Non-invasive method
- Multiple neurons excited together in a specific area
—> ***Electromagnetic fields generated by net effect of slow ionic current flow in neurons
Advantages (compare to fMRI):
- NO operational noise
- Better temporal resolution (with sub-msec precision)
- Subject can move their heads within MEG helmet
Disadvantage:
- Require magnetically shielded room
- MEG scanners require superconducting sensors (***SQUID: superconducting quantum interference device)
Neuroplasticity
- Remodelling of CNS
- Changes in neural pathway —> change in behaviour / sensation
- Plasticity greatest in developing brain
- Also observed in adults:
- For learning and memory
- After injury —> Phantom limb sensation
- spread of connections from surrounding cortical areas into region that had the amputated limb
—> re-organisation of synaptic networks
—> Cortical remapping of referred sensations in response to amputation / injury (e.g. stroke)
