Significantly, neurogenesis takes place in only one region of the hippocampus - the dentate gyrus. Our computational model [19] imparts a unique role to this region in encoding the specific details of episodic memories (Figure 1). Moreover, the constant neural turnover in the dentate region ensures that each new event is encoded uniquely, without interfering with previously or subsequently stored memories [18,19]. The associational pathways in the CA3 and CA1 regions of the hippocampus can integrate this novel experience into prior learning episodes and perform associative retrieval. The unique feature of the new neurons that enables them to generate distinctive episodic memories without interference is their turnover. This turnover relies on two processes: selective cell death, which eliminates redundant units, and maturation, which transforms young, plastic units into less plastic ones. Both groups are continuously replaced by neurogenesis; hence the turnover [20,21,23,24] (Box 1; Figure 2). Experimental manipulations that reduce the number of new neurons, such as irradiation (Box 2), have contributed further to our understanding of possible functions of neurogenesis in the normal brain. Although many hippocampus- dependent tasks involve different aspects of associative memory, not every task that requires the hippocampus also requires the new neurons (for a review, see Ref. [25]). For example, spatial learning by rats in the Morris water maze is disrupted by hippocampal lesions [26] but not by irradiation [27]. However, although irradiated animals learn the water maze at a normal rate, their long-term memory retention of the hidden-platform location is greatly impaired relative to that in controls when they are re-tested four or more weeks later [27]. This finding is consistent with predictions of our computational model [18,19] that the new neurons are important for forming highly distinctive memories for individual episodes, thereby protecting them against retroactive interference (Figure 1). In addition to this role in encoding specific details of events, the new neurons seem to be crucial for linking events across time when these events are part of the same context. Thus, animals that lack new hippocampal neurons show deficits on tasks that seem to require contextualmemory abilities, including trace conditioning [28], contextual fear conditioning [29] and delayed non-match to sample (DNMS) with long delays [29]. However, they perform normally on corresponding non-hippocampal control tasks: delay conditioning [28], cued fear conditioning [29] and DNMS with short delays [29]. Whereas our previous delay conditioning [28], cued fear conditioning [29] and DNMS with short delays [29]. Whereas our previous model [18,19] accounts for the role of the new neurons in forming distinct event memories, the data reviewed here suggest that these neurons also have a role in linking events across time when the events are part of a common context. A novel proposal for the role of neurogenesis in temporal context: the functional cluster hypothesis Understanding the role of the new neurons in temporal coding requires a more elaborate model. Traditionally, the hippocampus is thought to be responsible for associating multiple stimuli into a single episodic memory. Synaptic integration of multiple inputs carrying sensory information can occur via spatial summation of individual synaptic potentials in dendrites of granule neurons. Such synaptic responses are usually mediated by two principal types of glutamate receptors, AMPA and NMDA. AMPA is responsible for short-term interactions and NMDA for long-lasting changes in excitability, such as during learning. However, temporal summation beyond the range of milliseconds cannot be explained using traditional biophysical mechanisms. Temporal summation of events on the order of minutes, hours or days might be required to solve the learning tasks described here. Neurogenesis is ideally suited to encode such events; it is an ongoing process that begins with proliferation of neural precursors and ends with fully functional mature neurons (Box 1). One striking feature of proliferation is that it occurs in clusters. The dividing precursors are often seen in groups of 2-10 cells, tightly packed in the subgranular zone (SGZ) of the dentate gyrus (Figure 3). These clusters disperse along the SGZ within several days, presumably by migration and/or attrition due to cell death. Differentiation of cells within the clusters into neurons is characterized by the expression of specific proteins, extension of axons and dendrites, and synaptogenesis [30]. Importantly, the excitatory influences, in the form of depolarizing GABA-mediated responses, are formed long before the new neurons integrate with the dense inhibitory circuitry in the dentate gyrus, which enables new neurons to sustain much higher activity levels than mature granule cells [31]. Hypothetically, one can envisage 'waves' of neurons that respond to afferent stimulation and send impulses from neurons belonging to a cluster, via mossy fibres, to CA3 for association of their common inputs by CA3 axon collaterals. New neurons within a cluster, innervated by different perforant path inputs, will respond to different features of an event. Some will fire in response to persistent aspects of the environment, such as odours, stationary objects and boundaries, which we shall refer to as the context. Other neurons might respond to more transient aspects, such as a tone or a shock. The highly plastic new neurons will become tuned to this constellation of features and should respond consistently when they experience the same context again. Using plastic recurrent connections, targets in CA3 can link the transient features with the context, thus temporally linking items into a single episode. This enables cued recall of the entire event from a single item, which provides the basis of episodic-memory encoding and retrieval (Figure 2). The new neurons will then either die or mature and become less plastic, which will protect the memory from interference by later learning. Subsequent events could be encoded by other 'waves' of generations of new neurons. This 'functional cluster' hypothesis shares with previous models the assumption of 'superior plasticity' of the new neurons [18,20-22] and is consistent with a recently proposed model of a mechanism that separates ongoing experience into temporally tagged, unique event memories [32]. More specifically, the cluster model proposed here (not to be confused with the 'clustered plasticity model' of Govindarajan et al. [33], which is a single-neuron model) assigns a unique role to the clusters of cells born at approximately the same time and their impact on the encoding of event memories in CA3.

It's important to understand the characteristics of working memory when you're designing nearly anything that requires mental effort.
Without adapting learning experiences to the learner's cognitive architecture, instructional design is hit or miss.
Current research in this area is demonstrating that working memory (a theoretical structure) is a dynamic and flexible entity.

Working memory used to be called short-term memory. It was redefined to focus on its functionality rather than its duration. Working memory can be thought of as the equivalent of being mentally online. It refers to the temporary workspace where we manipulate and process information. No one physical location in the brain appears to be responsible for creating the capacity of working memory. But several parts of the brain seem to contribute to this cognitive structure.

Capacity

Working memory is characterized by a small capacity. It can hold around four elements of new information at one time. Because learning experiences typically involve new information, the capacity of working memory makes it difficult to assimilate more than around four bits of information simultaneously. The capacity of working memory depends on the category of the elements or chunks as well as their features. For example, we can hold more digits in working memory than letters and more short words than long words. The limitations on working memory disappear when working with information from long-term memory (permanent storage) because that information is already organized into [ chunks ] schemata. Schemata are higher order structures made up of multiple elements that help to reduce the overload on working memory.

Duration

Novel information in working memory is temporary. It is either encoded into long-term memory or it decays or is replaced. Unless it is actively attended to or rehearsed, information in working memory has a short duration of around 20 seconds. Similar to the capacity issue, it takes mental effort to hold information in working memory for an extended time and can also be a cause of cognitive overwhelm.

Interactions with Long-term Memory

There is a continuous transfer of of information between long-term memory and working memory-both retrieval and transfer. Information is retrieved from long-term memory into working memory in order to make sense out of new information. Information that we attend to and integrate into our knowledge structures is transferred or encoded into long-term memory.

Individual Differences

Current research demonstrates that individual differences in working memory capacity may account for differences in performance of information processing tasks, like reading and note-taking. In studies with children, those who have a poor ability to store material over brief periods of time (difficulties with working memory) fail to progress normally in tasks related to literacy. An individual's developmental age and level of expertise probably account for differences in working memory. For example, facilitating learning can be helpful for novices but detrimental to experts.

Cognitive Load

Cognitive load refers to the demands placed on working memory in terms of storage and information processing. Intrinsic load is caused by the nature of the learning task and extraneous load refers to the demands caused by the format of the instruction. Cognitive load theory states that traditional instructional techniques can overload working memory because they don't account for intrinsic and extraneous load. Instructional designers can facilitate learning by considering and accommodating different loads. Germane load refers to the demands placed on working memory when learners are engaged in conscious cognitive processing to construct schemata while acquiring new knowledge. Increasing the germane load can most likely assist the learning process.

Working memory

A psychologist reflects on it.

Alloway

'working memory' refers to the ability we have, because of our computer - the brain - to get hold of at any time,
to hold on to small amounts of information, to make it available for a sequencing task, to continually change the information presented, whilst keeping an 'eye' on whatever else is going on at the time, inside and outside the person.
Having new neurons in continuous production, called on to do all this , that disappear when their duty is done, means the brain does not fill up with more and more cells,with no room left.
whilst keeping an 'eye' on whatever else is going on at the time, inside and outside the person.
Having new neurons in continual production, called on to do all this , that disappear when their duty is done, means the brain does not fill up with more and more cells,with no room left.

The hippocampus area of the brain, in continuous neurogenesis at the right level of proliferation, is what enables th brain to is what enables people to update stored experience so as deal with the changing circumstances in their lives Working memory is a kind of mental workspace that is used to store important information in the course of our everyday lives.

A good example of an activity that uses working memory is mental arithmetic. Imagine, for example, attempting to multiply together two numbers (such as 43 and 27) spoken to you by another person, without being able to use pen and paper or a calculator.
First of all, you would need to hold the two numbers in working memory.
The next step would be to use learned multiplication rules to calculate the products of successive pairs of numbers, adding to working memory the new products as you proceed.

Finally, you would need to add together the products held in working memory, resulting in the correct solution.
Without working memory we would not be able to carry out this kind of complex mental activity: keeping in mind some information while processing other material. A minor distraction such as an unrelated thought springing to mind or an interruption by someone else is likely to result in complete loss of the stored information, and so in a failed calculation attempt.
As no amount of effort will allow us to remember again the lost information, the only course of action is to start the calculation afresh.
Multiplying larger numbers (such as 142 and 891) 'in our heads' is for most of us out of the question, even though it does not require greater mathematical knowledge than the earlier example.
Quite simply, the storage demands of the task are too much.

Are there limits to working memory? Yes.
It is unfortunately true that working memory is limited in a number of ways, and can easily fail us when we need it.
Here are some of the factors that lead to the loss of the contents of working memory:
l distraction
l trying to hold in mind too much information
l engaging in a demanding task


Working memory is the mental ability to hold small amounts of information in an active, readily available state for a short period of time, typically a few seconds
Cells from neurogenesisis - new cell formation - in the hippocampus are needed for this
Conversely, long-term memory involves storing a potentially unlimited amount of information for an indefinite period of time.
For working memory capacity, the two have to work together to function properly

Working memory used to be called short-term memory. It was redefined to focus on its functionality rather than its duration.
'Short term memory' simply refers to the storage of information (for a matter of seconds) without having to manipulate it in any way.
If we have to manipulate what we are holding in short term memory to complete a task or whilst doing something else at the same time,
we are using working memory.
This distinction is very important.

Working memory can be thought of as the equivalent of being mentally online.
It refers to the temporary workspace where we manipulate and process information. Because learning experiences typically involve new information, the capacity of working memory makes it difficult to assimilate more than around four bits of information simultaneously.

Novel information in working memory is temporary.
It is either encoded into long-term memory or it decays or is replaced. Unless it is actively attended to or rehearsed, information in working memory has a short duration of around 20 seconds. It takes mental effort to hold information in working memory for an extended time and can also be a cause of cognitive overwhelm.
The limitations on working memory disappear when working with information from long-term memory (permanent storage) because that information is already organized into schemata. Schemata are higher order structures made up of multiple elements that help to reduce the overload on working memory.

There is a continuous transfer of of information between long-term memory and working memory both retrieval and transfer. Information is retrieved from long-term memory into working memory in order to make sense out of new information. Information that we attend to and integrate into our knowledge structures is transferred or encoded into long-term memory. No one physical location in the brain appears to be responsible for creating the capacity of working memory. But several parts of the brain seem to contribute to this cognitive structure.

The capacity of working memory depends on the category of the elements or 'chunks' as well as their features. For example, we can hold more digits in working memory than letters and more short words than long words.

Prospective Memory is remembering to carry out intended actions at appropriate points in the future

We cannot hold living arrangements together without Prospective Memory [PM]

Even minimal reflection prompts the realization that the texture of our daily existence is inextricably bound to PM tasks.

Without PM you cannot move forward in life. You are left stuck with the experience and interests you had before schizophrenia arrived, Certainly updating particular interest preoccupation remains, but adding to general experience is too limited to put together a full routine in personal, domestic, social, and occupational living.


Working Memory Capacity is the total of all the brain neuronal connections that have to come to work together when there is an intention to do something , to complete the intention.

The idea of intending - say to have such and such a meal the next day - brings together now in mind , all the skill bits to do it that have been stored in memory during the lifetime - your experience - and adds now the new stuff that is required to prepare to be doing what you intend, now having decided on a particular task.

Executing the tasks that are to be brought into play, in the right order at the right time, to complete the intention, requires memory to be held on hand to allow access to what is required at every step .

Thel reduction in neurogenesis at the hippocampus does not give enough working memory span to do that . A critical part of the connection in the brain to the working memory system is the hippocampus area, one of only two areas in the brain that are continually making available new cells - neurogenesis .

Enough new cells must be kept replenished there in the hippocampus for memory to be held long enough, so that things that are perceived to matter go into a memory store,
that what is necessary from stored experience to cope with outside matters, such as when an intention to do something is actually to be done, can be called upon at the right moment

New cell making in the hippo-campus is reduced in schizophrenia. ( Reif et al 2006 .... )
That likely happens at the onset of the illness.

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Three studies on working memory in schizophrenia

1.
Gold et al

Sufferers from persistent schizophrenia steadied on standard medication were asked to recognise and place colour worded items,
declaring them at one second and four seconds after exposure

What was examined was the number of items :-
accurately stored
retained to be able to show them at 4 secs.
Schizophrenia subjects were as accurate as controls, but, they did not hold on to the items at 4 secs.
The situation at delay showed no deterioration of capacity nor of precision.
What they held was stored. But they did not store enough at first point.
' Visual WM representations are neither less precise nor more prone to decay in schizophrenia.

Instead, patients exhibit a reduction in the number of items they can concurrently maintain in WM '.
... quote ... " Patients show clear reductions in the number of items that can be stored in WM [ Ed Working Memory ] but no evidence that their WM representations are less precise or less stable than those of healthy individuals "
2.
This next also points to a remedy.
Van Raalten and colleagues [ Reference } found that, although the patients' learning ability was impaired when frequent information updating was required,
their capability to profit from practice under stable learning conditions was unimpaired.
" When encouraged and accompanied, given the opportunity to practice,
sufferers do store what they have memorised: equally as well as for 'control subjects"

by 'chunking'.
d.2
This study now confirmed :- This study now confirmed :- Koch et al
"... First evidence from studies with schizophrenia patients indicates that the potential to profit from short-term practice under stable learning conditions
( ie, when the same stimulus material is repeatedly being processed ) is largely preserved.
patients showed significant performance improvements and significantly reduced WM activity with increasingly successful processing.

3,

To test their memory hypothesis researchers [ Elvevaag et al: BMC Psychiatry 2003.3.0 research article open access ], based at NIMH and at the University of Warwick, compared the prospective memory of people with and without the disease.
In each test participants manoeuvred a ball around an obstacle course for 90 seconds.

The ongoing activity was a commercial battery-powered game ("Kongman"; TOMY Toy Corporation, 1982) in which a steel ball was to be moved around an obstacle course by pressing a button at the appropriate time points in order to open or close certain routes through which the ball could travel. Each game lasted 90 seconds, and participants were instructed to accumulate as many points as possible during each game until the time was up.

The Game commenced by each participant winding a timer at the base of the game. The game was sufficiently easy and enjoyable that participants engaged in the game and all participants performed extremely well.
[ i.e. the Study subjects with schizophrenia had rehearsed and so 'chunked' the game, and then did well on the basic test ... but then ...later ... ]

During the course of the game the timer moved from the start to the finish position ( taking 90 seconds ).
The rim surround of the timer was covered and colored with red and green colored paper, such that the first 25 seconds were red and the remaining 65 seconds green.

The Prospective Memory task was to turn a counter (a poker chip that was similar on both sides) over once during each game.
However, participants were instructed to turn the counter over only when the timer reached the green zone
(i.e., they could not respond prospectively immediately, but had to wait for some proportion of time into the game before responding).

were to play the game a total of 10 times (i.e., 10 trials). After each of the ten games, participants were asked if they had remembered to turn the counter over during the game. The experimenter employed a stopwatch to note the time at which the counter was turned over, and whether it was in the green or red zone. The participants' response to the question concerning whether they remembered to turn over the counter was also noted.

They were then asked [ the holding injunction ] to turn over a counter when they were at least 25 seconds into the test.

The time delay ensured that prospective [ i.e. recall for a future event ] memory had to be used.

Participants with schizophrenia were more likely to forget to turn over the counter.

At the end of the test the participants were asked if they had remembered to turn over the counter.

Approximately a third of the time participants with schizophrenia reported they had done so when they had not.

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