* Check the slides on Blackboard for an overview of the models

Memory

Memory is the ability to store information, to retain it and apply it later, both in recognition and reproduction. Semantic memory is the memory of facts, like words. Semantic memory is how our brain makes sense of the world and it can be compared to a living database. It helps us cope with new objects and new experiences. Semantic dementia, seen in the shown video, is the inability to distinguish one thing from another. It is caused by cell death in the left temporal lobe. Categories become more general. The patient is still able to identify ‘an animal’, but is having more trouble with identifying what specific animal it is. Semantic dementia results in problems with knowledge, not with language.

Models about the short term memory are designed by Baddeley and Hitch and by Atkinson and Shiffrin. These models will be discussed later on.

* Baddeley & Hitch model: short term memory

The model designed by Baddeley & Hitch consists of several components. The central executive controls everything that happens in the short term memory. It is in control of the incoming information streams and it guides every incoming information stream to the correct location to be processed more accurately. The visuo-spatial store holds information active (repeating) until it must be memorized or forgotten. The visual spatial sketchpad deals with incoming visual information. It functions as a filter, to determine what information must be kept. Visual information is often dominant. The phonological store also holds information active until it is memorized of forgotten. Think of repeating one’s phone number until you can write it down and then forget it. The phonological loop deals with incoming auditory information. This also functions as a filter to determine what information to keep and what not. The episodic buffer is a buffer with limited capacity. If incoming information is important enough, it will lead the information to the long term memory. The episodic buffer is also used when information is retrieved from the long term memory.

Baddeley used other senses, like smell and taste, to the model in 2012.

* Atkinson & Shiffrin model

According to the model designed by Atkinson and Shiffrin, environment is the factor which brings input into the sensory memory. When paid attention to these incoming stimuli, the information will be processed to the short term memory. When we rehearse something long enough, the information will end up in our long term memory. If you want to recall something you first have to take something from your long term memory to your short term memory, and then recall it. The rehearsal loop will help you remember information until it can be forgotten or memorized, like repeating a phone number until you have written it down, so you can forget about it.

* Long term memory

Long term memory consists of declarative (explicit) memory and procedural (implicit) memory. Declarative memory can be seen as the more common sense. It consists of semantic memory (facts) and episodic memory (personal events). Procedural memory are the things you need to do and you have learned at some point in your life. You do not need to think about doing it. Procedural memory consists of skills and habits (tying your shoes, learning how to play an instrument), priming (certain knowledge, connected to the semantic memory), classic conditioning and nonassociative learning (habituation and sensitization).

Additional types of memory are prospective memory and autobiographical memory. Prospective memory is a relatively new concept in research, yet highly relevant in daily life. It is related to planning and what is going to happen. It can be either time based (I have to call the doctor in an hour) or event based (When I pass the post office, I have to mail this letter). It can be impaired in a patient, but it is hard to measure, because a patient’s day can be planned, so then, during your testing session, have to come up with something like “Remind me to do something every 30 minutes”, but the patient may have a good estimate of when another 30 minutes have passed. Besides, during a testing session you can only measure one thing. Autobiographical memory is a part of episodic memory. It can be seen as one’s own perspective or self-projection. An example is seeing a childhood scene from your own location/perspective or from above, or to see a social scene from someone else’s point of view. It has further overlap with prospection, navigation and theory of mind.

* Memory systems are separate: how do we know?

There are multiple arguments to support the assumption that memory systems are separate. Functionally, the memory systems serve different purposes and have different functions. Pharmacologically, depending on the type of medication, the behaviour with regard to only one type of memory can change. Developmentally, we develop memory skills at different ages in our lives. Experimentally, you can manipulate conditions to affect only one form of memory (mirror drawing task). Neuroanatomically, scanning performances give different results. For each element we have different neuroanatomical areas.

Memory process

1. Registration
2. Encoding
3. Storage
4. Consolidation
5. Retrieval
6. Cognition

Problems can occur in each of these steps. It is important to figure out where problems occur, so you can intervene on the right process.

Forgetting is totally normal and good. You do not need to remember all the incoming information. The Ebbinghaus forgetting curve demonstrates that the more time passes, the more you forget.

Spatial cognition

Spatial cognition is the ability to measure the distance to X and to estimate the sizes of objects. It includes many cognitive domains. Many problems in neuropsychological patients are linked to the domain of spatial cognition, since many parts of the brain are involved.

The frontal cortex contains spatial working memory, spatiotemporal learning and information integration. The posterior parietal cortex is seen as the “where” pathway. It functions for egocentric coding, categorical relations (left hemisphere), coordinate relations (right hemisphere) and spatial localization and attention. Spatial perception is based in the visual cortex. The temporal cortex is seen as the “what” pathway and serves in shape and object recognition. The hippocampus serves in navigation behaviour, allocentric coding and object location binding.

There are different types of cells based in the hippocampus which contribute to visual perception. Place cells contribute to determining the specific location of X, border cells contribute to determining specific borders, head-direction cells contribute to determining a specific direction and grid cells, which are equally divided, contribute to scaling an environment.

Neglect

Neglect is the inability to see contralateral stimuli. It can be in the visual, auditory, tactile or proprioceptive domains. There are no perceptual or motor problems. Typical problems that occur within a patient with neglect are problems with getting dressed, eating, drawing/writing and reading. Different testing tasks for neglect are drawing exercises, bisection tasks, star cancellation (to cross out small stars), or a body space exercise (put post-its on one’s body and then ask them to remove all of them). Neglect is often due to damage in the right hemisphere. In the past scientists often thought it was a sampling error, but now they think neglect really does occur more frequently with right hemisphere damage. The right hemisphere is dominant for certain functions for both left and right.

Treatment is limited. Neglect often recovers naturally, but adjustment in daily life are necessary if natural recovery does not occur. Adjustments can be stimulating contralateral sides and function reorganisation. Sometimes prism adaption is used. These are glasses that shift the world for a number of degrees. After taking off the glasses the world has changed for a couple degrees. This is only a temporal solution.

Information integration (frontal cortex)

Information integration also links to egocentric coding (posterior parietal cortex) and allocentric coding and object location binding (hippocampus). Object-location memory is memorizing where something was left. It can be tested by a task with multiple drawn objects, to see if the participant has recognized anything shifting. Egocentric coding is using your own body to get a perspective, for example to recognize object X on your left. Allocentric coding is to code everything’s position and then memorize that, for example to memorize who is sitting where in a room.

Constructional apraxia

Constructional apraxia is having problems in planning and organizing in combining spatial aspects. It comes with action impairment and impairment is very difficult to determine. It is very rare and we don’t know much about it.

Types of spatial behaviour

Types of spatial behaviour are route following, piloting and dead reckoning. Route following is seen in ants when they find a food source: they will keep following that specific route which guides towards the food source. Piloting is exploring behaviour. Once you have found location X you will use your environments to find the location. Dead reckoning is registering your own movement.