Functional networks

Question 1

What is the scale of the brain?

Answer 1

· The primate brain is composed of about 1012 neurons
· Each neuron makes 103 connections with other neurons
· Information therefore flows in about 1015 connections!
Working out how such a system operates is a formidable task.

Question 2

What generalisations are there about the brain?

Answer 2

· There are ways in which the problem space can be reduced by looking for common principles. For example…
· Parallel vs. serial processing
· Convergence vs. divergence
Local vs. Distributed processing

Question 3

What are cortical networks?

Answer 3

· The cerebral cortex contains many ‘networked’ areas that process and exchange information
Understanding the architecture of these networks gives us clues about the architecture of function.

Question 4

How are cortical networks organised?

Answer 4

· Some networks appear to be organised according to a common hierarchical plan
· Large parts of these networks are ‘modality-specific’:
They process information related to only one type of input or output (auditory, visual, somatosensory, motor, proprioceptive etc).
Sensory inputs and motor outputs are ‘represented’ at different levels of abstractions at different levels of these networks.

Question 5

What is the gateway to the cortex?

Answer 5

· The thalamus is a subcortical structure composed of a collection of nuclei
· The cortex is reciprocally connected to the thalamus:
· Different areas send and receive projections to it
Sensory information arrives here before entering the cortex

Question 6

What are the 3 types of cortex?

Answer 6

· There are three general functional types of ‘cortex’
· Thalamus
· Primary cortex 
· Unimodal cortex
-Supramodal cortex

Question 7

What happens in the primary cortex?

Answer 7

· Initial level of cortical processing
· Low level information (least abstract)
· Activity is specific to one modality
Maps in the cortex: Topographic arrangement reflects physical parameters

Question 8

What happens in the unimodal cortex?

Answer 8

· Intermediate level cortical processing
· Intermediate level information
· Activity is specific to one modality
· Neural organisation is less topographic and reflects physical
parameters less obviously

Question 9

What happens in the supra modal cortex?

Answer 9

· High level cortical processing
· High level, very abstract information
· Activity is not specific to single modality, but to a type of information processing
Neural organisation reflects physical parameters less obviously

Question 10

What happens in the primary visual cortex?

Answer 10

· The retina projects to the lateral geniculate nucleus (LGN) of the thalamus.
· The LGN relays this information to the primary visual cortex
· The primary visual cortex is the first cortical area to process visual information.
Other names: V1, Area 17.

Question 11

What is Retinotopic organisation?

Answer 11

Different areas of the visual field are represented in discrete areas of the cortex.

Question 12

Primary cortices - Orientation selectivity:

Answer 12

· Neurons fire in relation to the orientation of a visual stimulus
Organised into orientation-specific ‘columns’

Question 13

What happens in the Primary auditory cortex ?

Answer 13

· Information is relayed to the medial geniculate nucleus (MGN) of the thalamus
· The MGN projects to the primary auditory cortex in the superior temporal gyrus of the temporal lobe
· The Primary Auditory Cortex is also called the ‘core’’.
· Cells fire in relation to different auditory frequencies and are mapped ‘cochleotopically’.
Cochleotopic neurons are arranged into three zones

Question 14

How does the primary motor cortex send information?

Answer 14

· Unlike the sensory system, the primary motor cortex sends information out to the spinal cord
· It is still a primary cortical area because it is at the lowest point of the motor hierarchy.
· When neurons are stimulated, different muscles groups on the ‘contralateral’ side are activated.
· The neurons are arranged topographically
· Neuronal recordings during movement: ‘population’ activity is related to the direction of the movement
Population activity in the motor cortex is related to the direction of movement

Question 15

Primary motor cortex: brain-machine interfaces?

Answer 15

· Understanding the low-level coding of the motor cortex finds practical uses
· Neural Prosthetics: Understanding information processing in the primary motor cortex allows scientists to develop methods that translate directly into benefits for clinical populations
This technology allows the brain to interface directly with control technology and bypass

Question 16

What was shown using monkeys and brain-machine interfaces?

Answer 16

· Neuronal ensemble activity recorded through a 96- microelectrode array implanted in primary motor cortex
· Intended hand motion modulates cortical spiking patterns three years after spinal cord injury.
· Decoders: A ‘neural cursor’ with which MN opened simulated e-mail and operated devices such as a television, open and close a prosthetic hand, rudimentary actions with a multi-jointed robotic arm.
· Technique based on intracortical neuronal ensemble spiking
activity could provide a valuable new neurotechnology to restore independence for humans with paralysis.

Question 17

What happens in the Unimodal visual cortex?

Answer 17

· There are a plethora of visual areas outside the primary visual cortex.
· These areas seem to be selectively responsive to specific visual properties.
Visual perception appears to use a ‘divide-and-conquer’ strategy in which processing is distributed and specialised.

Question 18

Are there visual systems outside of the PVC?

Answer 18

· There are a plethora of visual areas outside the primary visual cortex.
· These areas seem to be selectively responsive to specific visual properties.
Visual perception appears to use a ‘divide-and-conquer’ strategy in which processing is distributed and specialised.

Question 19

· Unimodal visual areas are distributed in the…

Answer 19

…occipital, temporal and parietal lobes
· They are networked into ‘dorsal’ and ‘ventral’ streams
· Information at each level of the stream becomes more abstract
· The dorsal stream (‘where’ pathway):
Extends into the parietal lobe
Processes location-related information
· The ventral stream (‘what’ pathway):
Extends into the temporal lobe
Processes object-related information

Question 20

· Auditory areas of the temporal lobe:

Answer 20

• (i) Core cortex (primary cortex)
• (ii) Belt cortex
  (iii) Parabelt cortex

Question 21

· Belt Cortex:

Answer 21

· Surrounds the core cortex

Receives projections from the core cortex •Composed of seven fields on the superior temporal gyrus

Question 22

· Parabelt Cortex:

Answer 22

· Surrounds the belt

Receives input from belt cortex

Question 23

Where does the Unimodal motor cortex send its outputs?

Answer 23

· Unlike sensory areas, unimodal motor areas send their outputs to the primary motor cortex and spinal cord.
· Areas of unimodal motor cortex are called ‘premotor’ areas.
· There are all in the frontal lobe
· There are several subdivisions

Question 24

· The premotor cortex consists of distinct cortical areas that receive inputs from the prefrontal cortex and send outputs to the primary motor cortex.
· There are three broad subregions:

Answer 24

· Dorsal (upper part on the lateral convexity)
· Ventral (lower part of the lateral convexity)
Medial (On the medial wall)

Question 25

What is the supra modal cortex also known as?

Answer 25

· Also known as ‘association cortex’ and ‘heteromodal cortex’.
· Neurons in these areas have very complex response properties
· Sensory- or motor-related neural activity is often dependent on context
· Areas include the prefrontal cortex, the parietal cortex, and some temporal lobe areas.
The cortical hierarchies terminate in supramodal cortex