Significantly, neurogenesis takes place in only one region of the hippocampus - the dentate gyrus. Our computational model  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. ). For example, spatial learning by rats in the Morris water maze is disrupted by hippocampal lesions  but not by irradiation . 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 . 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 , contextual fear conditioning  and delayed non-match to sample (DNMS) with long delays . However, they perform normally on corresponding non-hippocampal control tasks: delay conditioning , cued fear conditioning  and DNMS with short delays . Whereas our previous delay conditioning , cued fear conditioning  and DNMS with short delays . 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 . 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 . 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 . More specifically, the cluster model proposed here (not to be confused with the 'clustered plasticity model' of Govindarajan et al. , 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.
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.
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.
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.
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 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.
A psychologist reflects on it.
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.
Conversely, long-term memory involves storing a potentially unlimited amount of information for an indefinite period of time.
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.
we are using working memory.
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.
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 .
That likely happens at the onset of the illness.
Schizophrenia subjects were as accurate as controls, but, they did not hold on to the items at 4 secs.
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 "
This next also points to a remedy.
their capability to profit from practice under stable learning conditions was unimpaired.
patients showed significant performance improvements and significantly reduced WM activity with increasingly successful processing.
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.