PSYC211

Cognitive Neuroscience

Cognitive Neuroscience

The link between biology and psychology, studies the relationship between the brain and cognitive processes

Central Nervous System (CNS)

Composed of the brain and the spinal cord and is responsible for receiving, integrating, and coordinating information from throughout the body.

Peripheral Nervous System (PNS)

Made up of nerves located outside the brain and spinal cord, serves as a communication network between the CNS and the rest of the body.

Sub-divisions of the PNS

Somatic Nervous Systems (SNS) and Autonomic Nervous Systems (ANS)

Somatic Nervous System (SNS)

Deals with the external environment and is made up of afferent and efferent nerves.

Autonomic Nervous System (ANS)

Regulates the body’s internal environment e.g. heart rate, sweating, digestion of food and is also made up of afferent and efferent nerves

Afferent Nerves

Receive information (input)

Efferent Nerves

Generate behaviours (output)

Sub-divisions of the ANS

Parasympathetic Nervous System and Sympathetic Nervous System

Parasympathetic Nervous System

Maintains homeostasis, regulates vital processes in the body and leaves you in a relaxed state

Sympathetic Nervous System

Is responsible for activating the body's physiological responses to perceived threats or stressful situations due to arousal

Twelve Cranial Nerves

• Smell

• Vision (part of CNS)

• Eye movement

• Trigeminal - (facial sensation, mastication)

• Facial expression

• Hearing and balance

• Oral sensation, taste, salivation

• Vagus – heart, lungs, digestion

• Shoulder elevation and head turning

• Tongue movement

Spinal Nerves

• Cervical C1-C8

• Thoracic T1-T12

• Lumbar L1-L5

• Sacral S1-S5

• Coccygeal

Spinal Cord and Nerve Connections

The spinal nerves connect to the CNS through the spinal cord. Input comes in through the dorsal side and the output goes out from the ventral side

Forebrain

Made up of the telencephalon and the diencephalon

Telencephalon

Largest main structure in the brain and is where most of the processing is going on

Neurons

Brain’s primary processing units and controls what happens in the brain

How many layers are there of cortex

6

Features of a neuron

Made up of the cell body, dendrites, axons and synapses

Synapses

Sends information through different cells

Membrane potential of a neuron

-70mv

Critical charged ions in the cell

K+ (potassium) and A- (proteins)

Critical charged ions outside the cell

Na+ and Cl-

Concentration Gradient

Refers to the gradual change in the concentration of a substance across a space or region. It describes the difference in the concentration of a particular substance between two areas or compartments. Particles diffuse across the membrane then the concentration will try to diffuse and equalise

Info is transmitted:

within the cell by transient alterations in the membrane potential produced when ions are allowed to cross the membrane

Graded potential

Can be stimulated by sound, light, touch etc. Produces a small change in electrical potential. The bigger the input, the larger the change

Excitatory Post-Synaptic Potential (EPSP)

Results of the channels opening and sodium going into the cell. Depolarisation of the cell

Axon Hillock

The threshold level of intensity and action potential must cross to change electrical potential

Voltage gated sodium channels

Let sodium in and they respond to a change in potential from the inside and outside of the cell.

Hodgkin-Huxley Cycle

Explains how action potentials are generated in neurons by the movement of ions across the cell membrane

Myelin in the NS

Helps to speed up action potential propagation. Sections of axon that are covered in myelin and acts as insulation and has a conduction velocity up to 100+ m/s

Multiple Scleriosis

Is a result of demylenation where the myelin gets damaged so it means that the NS will be transmitting info slower

Retina

Group of cells that respond to light that comes in

Rods and cones

Cells that respond to photons of light

Intrinsically Photosensitive Retinal Ganglion Cells (ipRGC)

Utilise the photopigment melanopsin which is sensitive to blue light and are critical for controlling circadian rhythms

Blondspot in retina

The gap where there are no receptors, rods or cones located in the left eye

Cones

Photopic vision, high acuity colour vision in good illumination (best for day vision)

Rods

Scotopic vision, poorer acuity achromatic vision in low light levels (better for night vision)

Distribution of cones in retina

Highest around the centre of fovea and drop off in peripheral vision

Inhibitory Post-Synaptic Potential (IPSP)

Hyperpolarisation of the membrane

Lateral Inhibition

Lateral inhibition is a process in which the activity of neurons in the visual system is inhibited by neighboring neurons. It enhances the contrast and sharpness of edges in visual perception.

Electromagnetic Spectrum

The whole range of electromagnetic waves permeating the world

Different types of cones

Red, blue and green

Deuteranomaly

Colour blindness when you’re weak in green receptors

Protanopia

Colour blindness where you have no red receptors

Opponent Process Theory

Explains how colors and emotions are processed in the brain. It suggests that colors are processed in pairs of opposing colors, while emotions are processed in pairs of opposing processes. This theory helps explain color afterimages and the emotional experience of pleasure and pain.

Visual processing

Info from right visual field is processed on the left side of the retina and vice versa

Lateral Geniculate Nucleus (LGN)

90% of retina fibres travel here and it’s the nucleus of the thalamus

On Centre Cells

When you shine light onto the centre they will become active and start firing

Retinotopic Organisation

Visual world maps onto the retina and then to the LGN

Simple Cells in V1

Respond best to elongated bars or edges, are orientation selective, have seperate on and off subregions, can be monocular or binocular

Complex Cells in V1

Orientation selective, have spatially homogenous receptive field and are nearly all binocular

V1 Retinotopic Maps

Each point of the visual field maps onto a local group of neurons in V1, a remapping of retinal image onto cortical surfaces (retinotopy)

Cortical Magnification

When fixated on a central point of an image, we find that a large number of cells respond to the foveal region and far fewer cells responding on the outside

Topographic Organisation

An ordered representation of the sensory environment where spatially adjacent surfaces are represented in adjacent positions in the brain

Why topographic organisation?

Reduces the volume of the brain. If the brain gets too big it can lead to problems so reducing axon length provides space for more neurons and conserves metabolic resources therefore it facilitates processing e.g. opponent or lateral inhibition

Sound

A system that responds to waves in the air that are repeated pressure pulses at a particular frequency or wavelength

Sound system

The pressure pulses come through, impact on the eardrum, cause the eardrum to vibrate and that vibration is transmitted through the malleus, incus and the stapes where it is transferred mechanically to the end of the cochlea (the organ of hearing). In the cochlea there is a membrane and those vibrations will cause pressure pulses which causes the membrane to move and the receptors will respond to the vibrations and hair cells convert the mechanical energy into electrical energy. Inner hair cells are crucial for taking the vibrations and sending them.

Tonotopic Representation within the Cochlea

Low frequencies are  represented right in the depths of the cochlea and high frequencies towards the top. Where sounds are transduced pends on the frequency of the sound. Tonotopic representation is the transmission of tone or frequencies as a topographic representation.

Top Down Processing

Using information from higher-level mental processes and prior experience

Bottom Up Processing

Processing that begins with the sensory receptors

Dorsal Visual Stream

Uses visual info to guide body and space

Ventral Visual Stream

Identifying what objects are and information in the world

Cells firing in ventral stream

Response to Jennifer Aniston suggests that cells are very specific for certain faces. e.g. Halle Berry and Steve Carell Cells

Invariance in cell firing

Encoding a representation so that it is identified regardless of size, orientation, colour etc. The cell responds the same for each row of image whether it's been roasted or is in the left or right hemisphere as well as size and illumination. The cells aren't just responding in a template manner

Cell firing and familiarity

You are more likely to find cells that respond to people you know or see often

Gnostic/ Grandmother Cells (Local Coding Theory)

Break down cells into seperate pieces. One cell could fire for Jennifer Aniston but a completely different one could fire for Steve Carrel (either A or B)

Problems with Local Coding Theory

• Need to have a seperate cell for everyone, object and experience

• Susceptible to damage

• Perception of novel objects?

• Generalisation is difficult

• Pattern completion and generalisation require access to representations of other similar objects

Goals for visual information processing

• Separating Patterns

• Completing Patterns

• Allow for generalisation

Pareidolia

When presented with ambiguous info your NS interprets it as something else e.g. clouds as animals

Dense Encoding Theory

Rather than having one cell that represents your grandmother, you have groups of cells that represent face shape, hair, wrinkles dress and they communicate with each other to create a representation

Donald Hebb Organisation of Behaviour

Each psychologically significant event, sensation, percept, expectation, memory or thought is the result of a particular pattern of activity in a group of interconnected neurons (cell assembly)

Simple Cell Assembly in Brain

Neurons connected to each other in the brain and when we have a perception of an event we have cells that start firing.

STM- Hebb Organisation of Behaviour

A reverberating neural activity in a closed loop circuit

LTM- Hebb Organisation of Behaviour

Have to strengthen the connections between the neurons and these synapses would be strengthened and that would occur quite quickly in that short term period so at a later time you have a cue that makes it easier to recall

Reactivation

There is encoding of a visual image and when asked to recall later we can see activation in the brain in the same place from when you first encoded that information

Hebb' post and presynaptic cells

They fire together and the connection between them is strengthened and this allows the NS to associate inputs together

Long Term Potentiation (LTP)

produces long term alterations in the strength of synapses. Change in receptors and synapse shape after LTP

What does LTP depend on

The activation of the NMDA  subtype of glutamate receptor. To get this change in the strength of synapse you have to activate NMDA which gives you a change in synaptic strength

LTP and the Morris Water Maze

You have a big tank of water 1m x 1m and you put rats in the tanks and have a region thats just submerged under the water and you need to see that the animal is learning where the platform is. You take it out of the pool for one day then put it back in to see where they look for the platforms. This suggests you can block memories by using the same drugs that block LTP

How to test whether LTP has anything to do with memory

• show that blocking LTP prevent memory formation

• show that reversal of LTP produces forgettin

• show that learning leads to LTP-like changes

• show that producing LTP creates false memories or masks existing memories

V4

Involved in colour perception

V5

Involved in motion detection

Patient MP

Bilateral lesions of V5 her colour and form perception was intact but she had akinetopsia so had difficulty processing movements

What is the value of motion detection?

• Captures attention

• Helps segment the foreground from background.

• Helps compute the distance to various objects in the scene

• Helps in computing the 3D shape of an object.

• Allows estimation of the direction in which you are heading within the scene.

• Allows recognition and prediction of actions

How does the brain link particular features to the object they are associated with?

Temporal binding

Temporal Binding

• Distributed neural responses are tied together by the coordinated timing of their firing patterns.

• Cells firing in synchrony form cell assemblies that collectively represent a given object at a moment in time

• This shared timing tags specific cells as sharing the same “message” and links the features of an object together

Lashley (1929)

Thught that memories were distributed across the brain and held that view until the 1950s and patient HM

Patient HM

• concussed at age 9 and suffered seizures from age 10-16, did not respond to medication

• 1953, age 27, he underwent temporal lobectomy

• Scoville removed H.M.’s temporal pole, hippocampus and adjacent cortex bilaterally

• The number of seizures decreased but unfortunately he couldn't form any new memories and had good short term memory but bad long term memory

Patient HM post-operatively

• Severe anterograde amnesia

• Retrograde amnesia for about 2 years prior to surgery

• Intact short term and remote memory

• He described his experience as like living in a dream

• IQ improves

• He did not recognise his examiners despite being tested repeatedly for over 50 years

• Died in 2008

Mirror Star Drawing Task and Amnesiacs

As the days went on, HM got better at the task. He started with 30 errors and got better at it day by day. This indicates that something in his NS remembered how to do the task even though he didn’t

Declarative Memory (Explicit Memory)

Important for facts and events

What is involved in memory consolidation?

The hippocampus

Removal of the rhinal cortex (around the hippocampus)

Tests on individuals with HPC + Rhinal Damage had greater memory deficits on the Rey Osterrieth Figure Test and drew something unrelated

Patient RB

Had open heart surgey, had an ischemic episode which resulted in selective, marked anterograde amnesia and very minor retrograde amnesia. Temporal lobes seemed intact but found subtle damage in the hippocampus

Rey Osterrieth Figure Test

Shown a figure and asked to copy it and then half an hour later have to draw it from memory. Damage to the HPS produces a memory deficit which results in poorer performance

Patient NA

Young person who went to a military college and was into fencing and their roommate poked him into his nostril and it went into his brain and it had damage to the mediodorsal thalamus and mammillary bodies. As a result of this NA had anterograde amnesia and this suggested that these other regions connected to the hippocampus are important

Wernicke-Korsakoff Syndrome

Occurs in heavy drinkers, produces similar memory deficits to those that result from temporal lobe damage

Cause of Wernicke-Korsakoff Syndrome

Caused by lack of thiamine (vitamin B1) which affects the brain and nervous system, rather than by alcohol directly. Many heavy drinkers have poor eating habits, stomach lining becomes inflamed and can’t abosrb key vitamins

The Hippocampal-Diencephalic Memory System

Information flows up the fornix into the mammillary body across into the anterior thalamus and then out into the wider cortex. It turns out that memories depend on this circuit and memories are consolidated throughout the neocortex so Lashley was right in his thinking.