Differences > RAS vs Thalamus and Central Executive vs Episodic Buffer

[diligent18]

Could someone please explain the difference between the roles of the RAS and Thalamus, as well as between the roles of the central executive and the episodic buffer? What are the main differences we need to know? Different sources seem to be saying different things, and I'm becoming a little confused.

[Limista]

Distinguish between the RAS and the thalamus:

RAS:
* responsible for sustaining consciousness and mediating various levels of alertness and wakefulness through general arousal mechanisms (regulate sleep/wake cycle or transition period from being awake to being asleep)
* directing attention to sensory events (enormous amount of sensory information entering the brain, RAS limits amount of info available to brain by filtering out irrelevant sensory info before transmitting sensory impulses from body via thalamus to cerebral cortex)
* initial 'switching station' for sensory input

Thalamus:
* regulates levels of wakefulness and alertness due to receiving info about our state of arousal from the RAS
* final 'switching station' for sensory input, before it is redirected to primary cortex of relevant lobe for processing 

The RAS and thalamus do not work independently of each other. RAS influences levels of arousal and attention through thalamus, since it has ascending nerve tracts which connect to central areas of thalamus.

Central executive versus episodic buffer:
* two are totally different
Central executive: coordinates and processes info from phonological loop, visuospatial sketchpad and episodic buffer, as well as from LTM through link of episodic buffer
Episodic buffer: on instruction from the central executive, episodic buffer retrieves information from LTM to associate with info already in working memory, before selecting and encoding (recommitting) modified memory back into LTM.
The episodic buffer is like a flap that is ordered around by the commander (central executive) - this is just my colloquial analogy!

[diligent18]

Thanks for your reply, Starfish.
So sensory information is filtered twice, first through the RAS, and then through the thalamus?
Also, isn't one of the roles of the episodic buffer to integrate and bind together information from the phonological loop, visuo-spatial sketchpad, and LTM adding time sequencing to form an 'episode'?

[Limista]

Sensory info is filtered twice, first through the RAS, and then through the thalamus.

It does not integrate info from the phonological loop, visuospatial sketchpad and LTM - this is the function of the central executive. It does however BIND together this info

[diligent18]

Sensory info is filtered twice, first through the RAS, and then through the thalamus.

It does not integrate info from the phonological loop, visuospatial sketchpad and LTM - this is the function of the central executive. It does however BIND together this info

Thanks for clearing that up!

[HiddenUser]

Sorry I still dont get the difference between the Central Executive and Phonological Loop? Can you please elaborate.

[brenden]

Sorry I still dont get the difference between the Central Executive and Phonological Loop? Can you please elaborate.

Essentially the phonological loop is a temporary store for sounds (think of a phone when you hear 'phono'), so when you're sub-vocally rehearsing verbal information you're using your phonological loop.
The Central Exec. however, coordinates or integrates material from the slave systems of working memory. It makes the decisions and combines the loop and the sketchpad (I like to think of the Exec as the 'Big Boss').
For example, working out the price of 5 tins of Pringles, your C. Exec would decide that you need your 5 times tables, order the Buffer to retrieve these times tables from LTM, at which point the sketchpad might form the mental image of "5 x 2.45", the phonological loop might be in use "5 x 2.45, 5 x 2.45, 5 x 2.45" while the Central Executive coordinates that material and makes the decision as to how much those Pringles are going to cost you.
I'm really sorry if I just confused you more. I'm not used to explaining things without the use of my hands and verbal intonation lol.

[Limista]

Phonological loop:
verbal (words/numbers) or auditory working memory
it is the 'inner voice' or slave system of the central executive - a storage component of working memory along with the visuospatial sketchpad
stores (through sub-vocal maintenance rehearsal) and process a limited number of verbally spoken words/sounds up to 2 seconds (therefore able to retain meaning of sentence as it is said to us from beginning to end)

The central executive:
coordinates and processes info from the phonological loop, visuospatial sketchpad and episodic buffer, as well as from LTM through link of episodic buffer.

Hope this helps:)

[HiddenUser]

Holy crap while I was reading you answers I realised I worded my question wrong.

What I meant was Episodic Buffer not Phonological loop.

Sorry guys

[brenden]

Ohhh in that case, you would make the distinction between the two in that the Episodic buffer acts as a middle man between LTM and the other slave systems whereas the Central Exec is the decision maker.
As defined in Grivas, the episodic buffer is a sub-system of working memory that enables the different components of working memory to interact with LTM.

[pubsquash]

So in terms of irrelevant stimuli that doesn't require attention, does the RAS just filter it out so that it doesn't travel to the thalamus for further processing? Does the thalamus have a similar role? Because what I learned was that the thalamus decides whether information should be sent to the cortical areas by either processing it to the cortex, or inhibiting it (and thus blocking it so that it isn't sent to the cortex)

[Limista]

The thalamus does have a similar role to the RAS, however it is the final sensory filter. RAS is the intial sensory filter (switching station).