Behavioural Neuroscience Flashcards
Action potentials
- electrical signal that occurs when neurons are excited
- -A very rapid reversal (depolarisation) of the membrane potential of an axon is called an action potential.
- occur due to opening of voltage gated ion channels
Changes in air pressure from sound waves
We hear sounds when objects vibrate, which in turn causes air molecules to compress and rarefy (become more dispersed) leading to waves that travel away from the object at around 1,100 km/h.
-as it move away, the air pressured is reduced, we then receive these signal
Physical and perceptual dimensions
of sound waves
amplitude(intensity) of sound wave affect loudness (how tall it is)
frequency of a sound wave pitch (how many oscillations)
Accumulation of amplitude and frequency affect the timber (simple or compolex)
Middle ears
-Middle ear: consists of three tiny bones called ossicles. The malleus (hammer) is connected to the tympanic membrane. It transmits vibrations via the incus (anvil) to the stapes (stirrup), which is connected to a structure called the cochlea (snail), which is part of the inner ear.
Inner ears
-Inner ear: consists of the cochlea, which contains the receptors for analysing sounds. The cochlea is a bony structure, but it has two small membranes that form windows on its fluid-filled interior. The stapes is connected to the oval window. Sound waves that cause the stapes to move in and out move the fluid over receptors inside the cochlea. Because the cochlea is a closed structure, another membrane is needed to allow the fluid to move: this membrane is called the round window.
The cochlea
contains the basilar membrane runs along the length of the cochlear
The cochlea converts mechanical movement of the ossicles into fluid movement along the basilar membrane
Movement of stirrup against the oval window
The round window deforms to allow the movement
Transduction of auditory information in hair cells
cillia are linked toghter by tip link
these tip link also control K and Ca ion channels
-bend tot he left ( no signal, to the right 100% signal)
Spiral ganglion cells and the auditory nerve
- When the stereocilia are moved ion channels are opened which in turn cause receptor potentials in the hair cells. The hair cells secrete a neurotransmitter that triggers action potentials in neurons called spiral ganglion cells. The axons of many thousands of spiral ganglion cells are grouped together to form the auditory nerve
- The axons of auditory nerve neurons form synapses with neurons in the medulla (part of the brainstem), which in turn send their axons to other parts of the brain for further processing
Place coding of frequency
along the basilar membrane
- higher frequencies produce greater displacements of the basilar membrane toward its basal end, and lower frequencies produce more displacement at its apex
- Different frequencies of sound are therefore coded by the particular spiral ganglion cells that are active along the basilar membrane, and this information is transmitted via the auditory nerve to the brainstem and other parts of the brain
Characteristic frequency of
hair cells
- a hair cell have a specific frequency that it respond to
Pathway to auditory cortex
Auditory nerve-> Conclear Nuclei ->Superior olivary nucleus -> Inferior Conclius -> Medial geniculate nucleus -> Auditory Cortex
Tonotopic organisation of primary auditory cortex
The primary auditory cortex is located in a region of the temporal lobe called the superior temporal gyrus . Much of this cortical region is buried inside the deep fold of the lateral fissure, and is therefore not visible from a lateral view of the brain.
Just as the basilar membrane represents different frequencies along its length, so the primary auditory cortex is organised as a tonotopic map, with lower frequencies represented more anteriorly and higher frequencies more posteriorly.
Cochlear implants – based on knowledge of place coding
- Some people are deaf because of damage to hair cells
- electrodes inserted along the basilar membrane
- Stimulation causes spiral ganglion cells to generate actionpotentials
Cochlear implant challenges
- a large number of electrodes to reproduce sound well
- fast sound processors required to determine how much of each frequency is in the sound
- Especially with a large number of electrodes
- Not optimised for music
- Our brain loses the capacity to make sense of novel input as we age
Experience of someone with a
cochlear implant
- Helen lost her hearing at 2 from meningitis
- one of the first people to receive a cochlear implant
- Still has difficulty after successful implant
- Keep in mind the technology has improved
- people able to perceive sound more accurately
- some children learn to sing in tune and can acquire local accents
Extracellular microelectrode
recording
Normally, neural tissue is transparent, but if we inject dye into the cell bodies, we can actually see the cell bodies of these neurons and the processes the dendrites and axons.
we can see also in this microscope image. There’s a fine wire that’s been lowered close to one of these neurons, and this electrode, when it’s hooked up to an amplifier, can actually pick up small electrical changes.
They are associated with the activity in these individual neurons. And on the basis of this technique, it’s possible to understand how neurons at different stages of processing are transforming the signals that originate in the ear and that eventually how those signals will enable us to understand sounds in the world around us.
The electromagnetic spectrum
Our eyes detect the presence and pattern of light reflected off objects in the world. We are sensitive to a very narrow range of wavelengths in the electromagnetic spectrum, known as the visible spectrum. The visible spectrum extends from 380 nm to 760 nm.
Our ability to see these particular wavelengths depends on the fact that this wavelength of energy interacts with structures.
The photoreceptors in our eyes and enables enables them to convert those wavelengths into a neural signal.
-Its the brain that make us see color
The human eye
- Inside the skull the eye is held by a muscle know as extra ocular muscles. also help with pointing the eye to different direction (allow focus of attention)
- light from object will come through the cornea and the lens, and passing through the vitreous centre part of the eye. all of which are transparent
- the back of the eye is a sturcture called retina where photoreceptor (cell that convert light to neural signal) exist
The retina and fovea
- region of highly packed photoreceptor are called fovea, image have highest resolution
- light from lower visual will be process by upper retina and vice versa
- there is a region where ganglion of neuron bundle up to connect the eye with the brain, this region is the blind spot and there is no picture here
Cells of the retina
- Light must pass through ganglion cell and bipolar cell before reaching photoreceptor (all are relatively transparent)
- in photoreceptors, and then it’s converted into neural signal. The signals from these photoreceptors then go through bipolar cells out to gangling cells.
- lateral cell, horizontal cell (make multiple connection with photoreceptor) and amacrine cell (make multiple connection with the ganglion cell) exist in the bipolar layer which allow signal procession.
Transduction of light into
electrical signals in the retina
- stimulus cause the photo pigment lamellae of the receptor cell to become hyperpolarise (more negative) which cause the bipolar cell to depolarise
- enough depolarisation of bipolar cell lead to action potential to be generated by the ganglion cell toward the brain
Three cone types with different spectral sensitivities
there are three types of cones, each containing a photopigment that is sensitive to a different range of wavelengths within the visible spectrum.
1) Short-wavelength (S) cones – peak sensitivity at 440 nm (blue light)
2) Medium-wavelength (M) cones – peak sensitivity at 530 nm (green light)
3) Long - wavelength (L) cones – peak sensitivity at 560 nm (red light)
rod cell 496nm activate at dim light
Ishihara colour plates test for colour deficiencies (blindness)
• Deuteranopia • the green cones are absent • Protanopia • the red cones are absent 1 out of 12 men and 1 out of 200 female are red-green colour blind
Cone combination in the fovea
and periphery
in the central part of the of our vision, where we have most sensitivity, we actually have a closer coupling between the number of photo receptors and the number of ganglion cells.
As we move further away from the phobia, we find that we have a lower density of photoreceptors. But we also have more than one photo receptor, ultimately contributing to a single ganglion cells.
-leading to diference in spacial resolution
Interactions in the retina (retinotopic)
- Each ganglion cell responds to light stimulation of a small region on the retina
- Which comes from a specific location in the world
- Retinotopic As opposed totonotopic
Visual pathways to the brain
After leaving the eye the axons of retinal ganglion cells are bundled together to form the optic nerves(one for each eye).
These project posteriorly and medially toward the optic chiasm. Here, roughly half
the axons from the retina of each eye cross over to the opposite side of the brain. Axons from the temporal half of the retina of the right eye remain on the same side, but axons from the nasal half cross over to the left hemisphere adn vice vers
The Retinogeniculate Pathway
- The Lateral Geniculate Nucleus (LGN) contains six layers of neurons
- The inner two are magnocellular layers (info about fast moving object)
- The outer four are parvocellular layers(color)
- The koniocellular sublayers are found below each of the magnocellular and parvocellular layers involve in color peception
- Projects to Primary Visual Cortex in the Occipital lobe
- Associated with “conscious” perception
- A relay station?
- There are more fibres providing feedback to the LGN, than input from the retina may indicate more fuction
Centre surround receptive field
structure in the LGN
- Receptive fields of LGN neurons have a centresurround organisation
- ON centre – OFF surround
- OFF centre – ON surround
- Each LGN neuron responds to light stimulation of a small location in the real world
- Retinotopic
- We can record action potentials from neurons in the LGN
The Retinohypothalamic Pathway
- signal recing the Primary visual cortex signals are then going to be processed in the other visual areas at the back of our brain
- it’s those processes that give rise to our conscious visual perception
- here’s a type of ganglion cells in the retina that is intrinsically photosensitive. They have melanopsin which can covert light to a neural signal
Visual input pathway to the Primary Visual Cortex
- The conscious visual pathway involves retinal projections to LGN, and form there to the Primary Visual Cortex.
- The primary visual cortex (also known as visual area 1, or V1) is the first cortical region to receive axons from visual cells in the lateral geniculate nucleus.
- Area V1 in each hemisphere contains a retinotopic map of the contralateral half of the visual field.
Loss of conscious visual experience after a
unilateral lesion of primary visual cortex
- Damage to area V1 can occur after a stroke affecting one of the major arteries at the back of the brain, the posterior cerebral artery. Following rupture or occlusion, the neurons supplied by the posterior
- cerebral artery are starved of oxygen and glucose, and so are irreversibly damaged. If area V1 is affected, the patient will become blind to all visual stimuli arising to the contralateral side of their present point of fixation, e.g., damage to V1 in the right hemisphere will cause blindness in the left visual field. This disorder is called a hemianopia (loss of vision for one side).
- Patients with a hemianopia are normally aware of their visual loss and will take active steps to compensate for the problem
Retinotpic organisation of primary visual cortex
V1 has a very well-defined map (the retinotopic map) of the spatial information in vision. In humans, the upper bank of the calcarine sulcus in the occipital lobe has neural responses to light stimulation in lower half of visual field (below the line of sight), and the lower bank of the calcarine to the upper half of visual field.
Functional organisation of
primary visual cortex
-The striate cortex has a locally organized structure based on layers and modules.
Layers
-It contains neurons in 6 layers that receive input from the different LGN cell types and regions that process those inputs in other layers before sending signals to other visual areas.
. -Koniocellular input is received by sublayers 2 and 3 in the striate cortex, magnocellular input is received by sublayer 4C α , and parvocellular input is received by sublayer 4C β.
Modules
-The visual cortex is organized into roughly 2,500 modules containing approximately 150,000 neurons that analyses features contained in one very small portion of the visual field. The modules cover the entire visual field (like the tiles in a mosaic)
-The modules consist cells clustered according to colour and form. Most neurons located within the Cytochrome oxidase (CO) blobs receive input from one eye and are sensitive to colour. Neurons outside the CO blob (the interblob regions) are more sensitive to orientation, movement, and binocular disparity (depth), but typically do not respond to colour. This segregation for form and colour is partially maintained in the signals to other visual areas.
Specialized visual areas that receive input via the primary visual cortex
The primary visual cortex is divided into several functional modules or subregions, each of which contains neurons that have specialised properties for extracting specific information from the visual input.
1) Primary visual cortex (also known as the first visual area, or V1)
2) Area V4, which has neurons that are sensitive to the colour of visual inputs
3) Area MT, which is responsive to moving visual stimuli
4) Inferior temporal cortex, which contains neurons that are selectively responsive to complex objects and faces
The two-streams hypothesis of visual processing in the brain
- Proposed by Milner & Goodale (1992)
- Dorsal stream & ventral stream
- The ventral stream computes a detailed map of the world from visual input
- The dorsal ‘action’ stream transforms incoming visual information for action
- Also referred to as the “what and where” pathway
- Although the dorsal/ventral stream is more concerned with perception vs action
- The independence of the two streams has been overemphasised
- a large amount of crosstalk
Ventral stream functional modules
- Functions related to objects and visual recognition
- V3+VP - Further analysis of information from V2
- V3A - Processing information from contralateral eye
- V4 - Analysis of form; processing of colour constancy;
- V8 - Lateral occipital complex Colour perception
- LO - Object recognition
- FFA (Fusiform face area) - Face recognition, object recognition by experts
- PPA (Parahippocampal place area) - Recognition of particular places
- EBA (Extrastriate body area) - Perception of body parts
Dorsal stream functional modules
- Functions related to location and action
- V7 - visual attention; control of eye movements
- MT/MST (Medial temporal/medial superior temporal) - perception of motion; perception of biological motion and optic flow in specific subregions
- LIP (Lateral intraparietal area) - visual attention; control of saccadic eye movements
- VIP (Ventral intraparietal area) - control of visual attention to particular locations; control of eye movements; visual control of pointing
- AIP (Anterior intraparietal area) - visual control of hand movements: grasping, manipulation
- MIP (Middle intraparietal area) - visual control of reaching
- CIP (Caudal intraparietal area) - perception of depth from stereopsis
Colour processing pathway
Colour processing begins in the retina.
Some ganglion cells have selective inputs from the L, M & S cones.
This gives some ganglion cells cone opponency in the form of R-G, and Y-B.
These ganglion cells go on to form the Parvocellular stream (R-G) and Koniocellular (Y-B) streams in the LGN.
These signals are NOT the perceptual dimensions of colour.
• The contributions to to the centre and surround are selective for cone type
Damage to color preception
- Extracellular recordings in monkeys
- CO Blobs in V1 (and regions in V2 that they project to) and Area V4 is highly responsive to colour
- Subseqeunt work has shown that V4 is also responsive to changes in shape & curvature
- Damage to corresponding region in human cortex causes colour blindness Achromatopisa
- selective loss of colour perception but Form and brightness unaffected
- Damage to one hemisphere results in achromatopsia in contralateral visual field
- Likely to be rare because common causes of brain damage are likely to involve visuals areas other than V4
Orientation mapping in cat visual cortex by Hubel and Weisel
- Video footage of orientation selectivity in cat visual cortex
- from Hubel and Weisel’s lab in the
- Major breakthough in our understanding of what the visual parts of the brain do
- Nobel Prize discoveries
Motion processing pathway at lower level (what stimuli do they respond to)
• Retinal ganglion cells and LGN neurons respond to moving stimuli
BUT
• stimulus could be moving in any direction
• stimulus could even just be turning off and on
• Although Magnocellular neurons are particularly responsive to motion…
• Cells in V1 are orientation selective
• Respond to moving bars or edges with specific orientation (but movement in either direction)
• Some only respond to edges or bars moving in one direction
• Still not good enough to account for perception of motion
MT neurones influence the perception of movement
Area V5 of the extrastriate cortex (also known as area MT, for medial temporal-temporal) contains neurons that respond to movement. Damage to this region severely disrupts a monkey’s ability to perceive moving stimuli
Visual neurons that are sensitive to visual motion may gradually adapt when exposed to a continuously moving stimulus, so that when the motion ceases a motion aftereffect occurs (as in the classic waterfall illusion). The effect does not occur due to adaptation of cells in the retina, since adapting one eye to the moving stimulus and then using the other eye to view a stationary surface still yields a motion aftereffect.
MST role integrates local motion
- The medial-superior-temporal(MST) area in the monkey has neurones that are sensitive to optic flow e.g. movement of the world cause by self motion. responsive to complex movement e.g. spiral motion. associated with the perception of biological motion (structure from motion)
- global integration of local movement consistent with a person or animal
- Analogous brain regions in humans
- We can decode age and gender from the dots!
Motion blindness (akinetopsia)
- Caused by bilateral damage to MT
- Rare due to small size and location of MT
- Case of LM
- sees the world is snapshots
- Unable to judge speed and therefore predict future position of moving objects
- Over filled tea cups
- Danger crossing the road
- BUT could see biological motion
- so MT is not involved in perceiving structure from motion
How can the brain build a neuron that responds to an object in the visual field (talk about shape n stuff)?
- A key aspect of our conscious experience is recognising familiar objects around us
- Primates (and other animals) rely on visual recognition to survive
- either by finding food or avoiding danger (being food)
- Scenes consist of light patterns with features that can be identified at lower levels of visual processing
- Bars & edges
- LGN & V1
- But what happens at the next level?
