Shimamura (2000). The role of the prefrontal cortex in dynamic filtering

Shimamura, Arthur P. (2000). The role of the prefrontal cortex in dynamic filtering. Psychobiology, 28(2), 207-218.

"four prominent aspects of executive control--selecting, maintaining, updating, and rerouting information process. These four aspects are couched in terms of dynamic filtering theory, which proposes that the prefrontal cortex acts as a selective gating or filtering mechanism that controls information processing."

"Lesions in the ventral region produce an abnormal perseveration of central sets.  A hallmark feature of this deficit is an inability to shift sets in object reversal and go/no-go tasks.  In such tasks, the animal must inhibit an incorrect but dominant response tendency.  In human studies, set-shifting tasks have been used to assess the ability to disengage from one tasks and perform another."

For instance, being delusional--self-centric, everything is about mes, myselves, and Is--is a dominant response tendency... hard wired.  

"Neuropsychological studies of patients with frontal lobe lesions and functional neuroimaging studies of neurologically intact individuals suggest that the dorsolateral region is involved in tasks that require various control processes, such as stimulus selection, working memory, memory retrieval, and set shifting.  Executive control is presumed to enable top-down "supervision" of cognitive processing at various stages, such as perceptual analysis, short-term memory, and response selection."

Aspects of executive control

Selecting activity and focusing attention

"Selective attention refers to the focusing of attention to perceptual features or to information in memory."

1. Stroop-like effect
2. Flanker task

"It may be that perceptual or response filtering is less a purview of the prefrontal cortex and is more associated with the anterior cingulate cortex.  Perhaps, selection of information in working memory may be more rooted in prefrontal processing.  In summary, neuropsychological of the anterior cingulate cortex in filtering perceptual or response modes, and there is some evidence for a contributory role of the prefrontal cortex in supporting these functions."

The question I have is... sensory memory is theoretically a store only... nothing gets manipulated.  Bearing in mind Chi's notion or "meta or not," where only second-order is only considered meta.  Wouldn't it make it sound like the executive control is but simple executive control?  Or, if thinking of it the other way, the executive control comes out of the box (sensory memory), from the perspective of the box, that should be meta enough?

Maintaining activity in short-term memory

"Smith et al. found increased left-hemisphere activation for object short-term memory [BA 37], but increased right-hemisphere activation for spatial short-term memory [BA 40]."

"Separate pathways for spatial and object information processing... though it is important to note that both separation and integration of these cortical streams may be critical for executive control."

Updating activity: manipulation of information in short-term memory

"Updating concerns the ability to alter activity levels among items in short-term memory.  Thus, rather than merely maintaining activity, updating involves top-down reorganization of activation levels."
"Failure to monitor and update information leads to perseverations."

Could my perseverance with this DWM book thing be an indicator of the failure to update? 8-O lol sigh

"Efficient learning involves the reorganization of sensory information into meaningful or conceptual representations.  This process requires the integration of new information with existing knowledge.  As such, learning must involve updating and organization of both sensory information and existing knowledge."

Albeit my difficulties in learning in general, my new psychotic symptoms apparently have no difficulty integrating themselves with the old ones stored in LTM... independent of my contribution... almost reaching the state of automaticity... I guess. 8-X

Sources memory...

I could never remember author names, years, and also have problems with terminologies... though I know the concept... even before my psychotic years...  

"Findings from both neuropsychological and neuroimaging studies suggest that the prefrontal cortex is prominently involved in both short-term and long-term memory tasks that involve the updating of memory activations.  In these tasks, it is necessary to rearrange or modulate the level of activations in short-term memory."

Rerouting activity: implementing set shifting

"One aspect that makes rerouting a particularly complex executive function is the need to disengage from and shift to different processing modes... Such internally mediated or volitional shifts in processing may be particularly demanding on executive control processes.  Indeed, rerouting requires shifts in stimulus activations, stimulus processing, and response programming.  As such, it represents one of the most complex forms of executive control."

When reading this section, I thought of the notion of ADL and IADL.  Sure, disruption in the ability to reroute activity/plan switching is an indicator of my head not working too well.  Yet, when is the head most disabled?  When you are struggling with the most basic task... attention.  In a sense, singing Diva's Lament about the inability to reroute from the dominant set called the delusional mental model?  Call it a blessing. 

Dynamic Filtering Theory: A theoretical account of Prefrontal Function

"At the cognitive level, such terms as central executive and supervisor suggest a rather intelligent control mechanism that oversees and manages information processing."

"It is proposed here, that the prefrontal cortex operates as a dynamic filtering mechanism that maintains selected neural activations and gates extraneous or irrelevant ones.  According to this view, at any given moment cortical and subcortical activations involved in sensory and cognitive functioning produce a cacophony of neural signals. The prefrontal cortex, with its extensive projections to and from many cortical and subcortical regions, orchestrates these signals by means of a filtering mechanism that inhibits some signals and maintains activation of others.  In essence, the prefrontal cortex acts to refine activity and increase signal-to noise ratios.  This mechanism may be particularly involved in inhibiting or damping extraneous activity, or "noise." under conditions of extensive interferences."

"Dynamic filtering theory suggests that activation in the posterior cortex initiates a pattern of associated activations in the prefrontal cortex.  By way of reciprocal projections back to the posterior regions, this pattern of activation enables certain neuronal ensembles to be kept active and others to be gated or inhibited.  This mechanism affords a means by which information processing in the posterior cortex can be maintained and modulated by signals from the prefrontal cortex.  Without prefrontal control, the system is subject to greater noise from extraneous activations."

Noise is an interesting concept.  Take my auditory hallucination for instance... the voices could get so busy at work that there is no moment of quietness.  Then, think about it... how does it work... the tuning down of the voices through meds or my blocking the voices in the back of my head (when possible)?  Like what was spoken before... something like at which level does the message get lost or distorted because of the noise--with the message as the reality shared by the others and the noise, psychotic version of reality?  What and where is the threshold etc.?

"Efficient temporal processing may require the clipping of recent active information as a way to segregate neural processing from one moment to another... reflecting an inhibitory signal back... a neural "inhibition of return," which could facilitate attentional shift.  Without this simple control, the system might be subject to perseverations of recent activation."

"Perhaps through experience, we acquire not only a vast amount of knowledge but also a multitude of filters that enable the selection of that knowledge."

"The word animals would not only activate representations in posterior cortical areas but also activate filters in the prefrontal cortex, which then would select, maintain, and modulate associated posterior activations."

Similar to the notion of security software.

"aspects of selection may involve modality-specific processing (e.g., sensory processes), whereas updating and rerouting involve polymodal processing"

Executive Control Process	Related Concept	Benchmark Task	Filtering Mechanism
Activation
Selecting	Selective attention	Stroop	Filter selection
Maintaining	Short-term memory	Digital span	Filter persistence
Manipulation
Updating	Monitoring	n-back	Filter switch-stimulus
Rerouting	Set shifting	Task switching	Filter switch-response

"The notion of selection is less controversial than the notion of active inhibition.  However, some physiological evidence suggest that the prefrontal cortex engages inhibitory control of posterior cortical activity.  Knight and colleagues studied event-related potentials (ERPs) in patients with dorsolateral prefrontal lesions.  In one study, the amplitude of evoked responses presumed to be generated in the primary auditory cortex was potentiated in patients with prefrontal lesions.  Thus, there appeared to be a disinhibition of posterior cortical activity as a result of a frontal lobe lesion."

Hello, World!  My auditory hallucinations!

Regardless the experts' general opinions on inhibition, there is something to the notion of inhibition.  There is a qualitative difference between simply amplifying the signals to attend on and with the amplification coupling with signal inhibition... if what I perceive is the manifestation of inhibition.

Since the notion of Central executive is in the context of working memory and, as mentioned earlier, sensory memory only a store, does this make this executive control worth the meta tag?

"This inhibitory control mechanism may filter or gate sensory information at very early stages of processing."

"Prefrontal regions are performing the same neural function--dynamic filtering--but different behavioral outcomes occur because different prefrontal regions are filtering different posterior cortical regions, which themselves serve different cognitive functions."

"Filtering problems may occur at many levels of information processing, including sensory processing, memory activation, and response selection.  At the level of sensory processing, prefrontal (and anterior cingulate) function may involve the selection and maintenance of sensory signals."

"Demands on dynamic filtering will occur to the extend that irrelevant activations intrude on information processing, such as in tasks involving dominant responses that must be inhibited.  In fact, the ability to inhibit previously dominant memory activation is an important feature of prefrontal control."

How I am wrong.

Emotional control and orbitofrontal cortex    

Metacognition and affect

Dynamic filtering theory in relation to other views

"Dynamic filtering theory offers a neural-based mechanism that enables top-down control of information processing.  This view builds on earlier theories of prefrontal functions... Baddeley's characterization of working memory and the central executive emphasizes activation and maintenance of information in short-term memory... Dynamic filtering theory is consistent with these views in suggesting that the prefrontal cortex is involved in selecting and maintaining activation in short-term memory."

Thank God... thought my low-latent inhibited head was seeing Central Executive... till I see it put down in black and white by the author himself... lol

"Mid-ventrolateral regions are presumed to be involved in first-order executive control processes associated with selection and maintenance of short-term memory.  Mid-dorsolateral regions act as second-order executive processes involved in monitoring and manipulation."

"However, there may be even further, more detailed ways to define the manner in which filtering can affect information processing."

"In terms of behavioral outcome, it is extremely difficult to differentiate a model based purely on selection from a model based on both selection and inhibition.  In the end, the two models can often lead to similar behavioral outcomes."

Again, from the psychotic perspective, there is a qualitative difference although, out of the mouth of a thought-disordered psychotic, a paradoxical notion.

Adaptive resonance theory: analogous to center-on, surround-off receptive fields.

How I am wrong... center on, surround also on.