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Reaction time
Choice reaction time is typically between 350-450 ms
Central nervous system
brain and spinal cord
Peripheral nervous system
the sensory and motor neurons that connect the central nervous system to the rest of the body
Somatic nervous system
Division of the PNS that controls the body's skeletal muscles.
Afferent
Input to a nerve
Efferent
output of a nerve
Cranial nerves
12 pairs of nerves that carry messages to and from the brain
Spinal nerves
31 pairs go in and out of brain, come in through dorsal (back) side and leave through ventral (front) side
Forebrain
Telencephalon - Cerebral cortex Diencephalon - subcortical
Six layers of neocortex
Molecular, External granular, external pyramidal, internal granular, internal pyramidal, multiform
Neurons
a nerve cell; the basic building block of the nervous system
Neruons - voltage
Have a negative membrane potential of -70mv while resting
Flow of ions across the membrane causes changes in potential, which creates and electrical impulse
ions involved in action potential
Sodium enters the cells, potassium leaves
Sodium concentration
Concentration gradient of sodium is into the cell Electrical gradient for sodium is also into the cell
Depolarisation
The change from a negative resting potential to a positive action potential (caused by opening of sodium channels)
Graded potential
a membrane potential that varies in magnitude in proportion to the intensity of the stimulus
Action potential
the change in electrical potential associated with the passage of an impulse along the membrane of a muscle cell or nerve cell.
Ion channels
Voltage gated sodium channels A certain voltage is required for them to open causes a positive feedback loop
Hodgin Huxley Cycle
Synaptic potential → membrane depolarises → voltage-gated ion channels open → Na flows into neuron → positive feedback → membrane depolarises
sodium-potassium pump
a carrier protein that uses ATP to actively transport sodium ions out of a cell and potassium ions into the cell
Action potential propogation
Travels along axon Travels at 0.5 to 2 metres per second
Myelin
a fatty substance that helps insulate neurons and speeds the transmission of nerve impulses Strength of action potential is boosted in nodes of ranvier boosts signal to 100m/s
multiple sclerosis
myelin sheath destruction. disruptions in nerve impulse conduction
The retina
the light-sensitive inner surface of the eye, containing the receptor rods and cones plus layers of neurons that begin the processing of visual information
Rods + cones
Named by their shape Cone mediated - high acuity colour vision in light Rod mediated - low acuity monochrome, in dark
Convergence
Cones - fed into their own individual bipolar and retinal ganglion cells
Rods - multiple rods connect to bipolar into fewer retinal ganglion cells
Distribution of rods and cones
Cones are situated in the middle of retina (macula, fovea)
Rods are mainly situated everywhere else
Number of photoreceptor cells
about 120 million rods about 6 million cones
Photosensitive retinal ganglion cells
Some ganglion cells use melanopsin to detect blue light These induce circadian rhythm Situated at bottom of eye, so they are more responsive to light from the sky
Neurotransmission
Release of chemicals across the synaptic cleft Most retina cells release glutamate, which is excitory Amacrine and horizontal cells release GABA which is inhibitory
opponent-process theory
Parts of nervous system suppress others that give competing information
complex cells
Visual cells in V-1 that respond to lines Many different specific receptive fields
Primary visual cortex
Where 90% of visual information goes first after LGN First characterised by David Hubel and Torsten Weisel
Simple cells
Cells in V1 that respond to line, or gradient, oriented in particular direction
Complex cells
Cells in V1 that give best response to moving lines of particular orientation
Cell hierarchy - visual system
Many ganglion cells feed into fewer LGN cells, which feed to fewer simple cells, leading to fewer complex cells
Columnar architecture of V1
Varying regions of V-1 respond to lines in different orientations
Retinotopic mapping
An arrangement of neurons in the visual system whereby signals from retinal ganglion cells with receptive fields that are next to each other on the retina travel to neurons that are next to each other in each visual area of the brain
Top-down processing
Cortex makes assumptions about the environment and fills in gaps
bottom-up processing
analysis that begins with the sensory receptors and works up to the brain's integration of sensory information
Parallel pathways
From v-1 information is split into the dorsal and ventral streams Ventral stream is concerned with implication of objects
v-5 motion
Ventral stream goes to V-5 Focuses on how an object is moving Cells have a preferred direction and speed
Neurological evidence of V-5
People with bilateral damage of V-5 develop akinetopsia The failure to perceive motion
What motion detection is used for
Capturing attention Computing shape of 3-d objects Estimation of direction Optic-flow: pattern of apparent motion
Sound
Pressure pulses we perceive to carry information Humans hear from 200-20,000 Hz
Cochlea
Where sound information is received Has a tonotopic map
Hair cells
Respond to movement Mechanical movement causes ion change and electrical impulses
Outer hair cells
Auditory receptor cells in the inner ear that amplify the response of inner hair cells by amplifying the vibration of the basilar membrane.
Inner hair cells
neurons in the cochlea; responsible for auditory transduction
Parallel pathways - audition
Nervous system splits into high and low frequencies This may be because large objects tended to be a threat - evolutionary
Top-down influences on A-1
66% of information to auditory complex comes from other cortical regions Helps fill in blank spots
The McGurk effect
Sound is affected by how we see people pronounce it
Representation of complex features
Occurs in ventral stream Places like inferiotemporal cortex
inferiotemporal cortex
Some cells in this area on respond to certain orientations of faces
Jennifer Aniston cells
Rodrigo Quiroga Some cells seem to respond only to Jennifer aniston This suggests every object we can perceive has it's own cell
Problems with Grandmother cells
It requires too many cells Susceptibility to damage - if cells are damaged you couldn't perceive that object anymore How do you perceive novel objects? What's the chance they found a Jennifer Aniston cell using just a couple hundred images?
Distributed encoding
The identification is spread across many cells All cells respond when you see the object
Sparseness
Sparseness of Grandmother cells maximises memory, but there is a big trade off with generalisabiltiy
Recent evidence for recognition network
Doris Tsao Recorded face patterns through temporal lobe Mapped a face and saw how neurons responded to changes
Binding
How the brain pieces information together Convergent hierarchical encoding vs. temporal binding
Convergent Hierarchical Coding
Cells firing for each feature of an object converge on a common target cell that is representative of those collective features
Potentially faster but inflexible and hardwired, ineffective for coding modified or novel objects or experiences, requires massive neuronal resources, and susceptible to damage
Temporal binding
Features that occur together in time are more likely to be related
Distributed neural responses are tied together by the coordinated timing of their firing patterns
This synchrony can be associated with repeated, oscillatory activity -Cells that fire together, wire together
Schizophrenia
a group of severe disorders characterized by disorganized and delusional thinking, disturbed perceptions, and inappropriate emotions and actions
two-hit model of schizophrenia
Developmental issues + environmental factors Now thought to be a neurodevelopmental disorder
Effects of schizophrenia on brain
Enlarged ventricles Reduction in size of regions: frontal cortex and medial temporal lobe Excessive subcortical dopamine activity Changes in GABA neurotransmission
The dopamine hypothesis
Drugs that increase dopamine can give schizophrenia symptoms Over activation of nucleus accumbens produce positive symptoms of schizophrenia
The glutamate hypothesis
Manipulating the glutamate system has a broad effect on schizophrenia
Coherence
Neurons firing together at the same time People with schizophrenia have lower frequency osscilations of neurons
Auditory steady state response
Ossicaltions can be induced with sound ASSR is reduced in patients with schizophrenia At 20Hz neurons tend to fire twice
Donald Hebb
Wrote the organisation of behaviour Theorised that any event causes a pattern of activity within the neurons
Short term memory
Neurons fire in a closed loop reverberating manor
Long term memory
Neurons fire in a closed loop with consolidated synapses
How connections are strengthened
Donald Hebb Post-synaptic and pre-synaptic neurons fires at hte same time "cells that fire together, wire together" Allows for association of inputs
Fear induction
Pain neurons firing at the same time as neurons representing visual stimuli creates fear Crab example
Long term potentiation
an increase in a synapse's firing potential after brief, rapid stimulation. Believed to be a neural basis for learning and memory.
Why does LTP occur?
Extra stimulation causes glutamate to bind to NMDA receptor and the ion channel associataed opens and lets Mg2+ out and Ca2+ in
How to test LTP
Rat in a pool tries to find platform Those with NMDA antagonist do much worse Over activation of LTP also confuses rats
Rat on a turntable
Drug developed to turn off LTP Maintainence of LTP requires kinase ZIP causes it to decay Rats could lose memories
Mass action
The cerebral cortex acts as one in many types of learning
Equipotentiality
the idea that memory is distributed throughout the brain rather than confined to any specific location
other parts of the brain can adapt if areas are damaged
Karl lashley
Patient HM
A patient who, because of damage to medial temporal lobe structures, was unable to encode new declarative memories. Upon his death we learned his name was Henry Molaison.
HM's deficits show
Dissociation of intelligence and memory Dissociation of declarative and procedural memory Hippocampus, medial tmeporal lobe structures involved in memory
Patient RB
Ischaemic episode during open heart surgery Selective, marked anterograde amnesia and very minor retrograde amnesia Rey-osterrith task showed RB has a little bit of memory present
Patient NA
Had a mini fencing foil shoved up his nose Anterograde amnesia + visual learning deficits