The neural activity that occurs early on in the working memory probing period is referred to as the FN400 (frontal negativity), as negative voltages are present in the frontal regions and generated in part by the left temporal regions. FN400 is associated with familiarity, recognition and modulating by neural instructions about relevant information to attend to, indicating a correlation to attentional processes as well. Larger FN400 amplitudes are associated with greater memory strength. 

Neural processes of working memory (WM): FN400 activity

Research suggests Alpha oscillations in brain regions with functions not engaged by a current task, must perform processes that inhibit activity in such non-relevant regions, as effective working memory functioning is dependent on inhibition of irrelevant processes. Neural activity during WM delay-test periods (when individuals are shown a black screen) show increased upper alpha power in parieto-occipital electrodes located above areas of the brain responsible to visual processing. A sustained high power of alpha activity is suggested to illustrate suppression of cortical gain, as opposed to low alpha power which reflects increases in gain. Thus high power alpha suggests top-down inhibition of brain region processes that are not relevant to a current task. Increased alpha activity is associated with decreased fMRI blood flow in the visual cortex, demonstrating the suppression of disruptive activity, thusly leading to facilitation of working memory performance. 

Neural processes of working memory (WM): Alpha activity

Neural activity measured during working memory (WM) performance shows increased theta activity in fronto-midline electrodes, a neural signal that suggests to be generated by the anterior cingulate cortex (ACC) and is reflective of an attentional mechanism facilitating selection and activation of relevant task-specific neural processes required to achieve a the current goals for enhancement out of multiple competing neural processes.

Neural processes of working memory: Theta activity

-	FN400 activity
-	Alpha activity
-	Theta activity

Syracuse University

There is converging functional neuroimaging evidence for the involvement of the sustained activity in the prefrontal cortex underlying the process of working memory during the delay period in a working memory task. And due to the fact that the PFC has a lot of cortico-cortico connections and coritco-subcortico connections, it might be the case that these different connections probably mediate different component processes of working memory. It has been believed for example the the cortical network might mediate the maintenance of goals, while the subcortical networks mediates response selection and motor control

The Neural Basis of Working Memory

It has been proposed that the different subdivisions of the PFC may be responsible for maintaining different types of information. Emergence of "what" and "where" pathways. 
Ventrolateral PCF >> nonspatial information, eg. object's shape
Dorsolateral PFC >> spatial information, eg. object's location

Subdivisions within the PFC - Information type

Ventral PFC >> were information is initially received + comparisons between maintained information
Dorsal PFC >>Information monitoring and manipulation

Subdivisions within the PFC - Operation Type

- Oculomotor Delayed Response Task
- Controlling Response Selection 
- During a working memory delay one can either 1. look back at a past event, or 2. look forward to a future event
- Masking pattern to disrupt iconic visual memory

Coding Schemes for Working Memory Mechanisms 

Oscillatory activity is modulated in these brain regions

•	Prefrontal region

•	Parietal region

•	Medial temporal region


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