Attention, Working Memory, and Executive Function[Processes Under Construction]

Graham Williams and Stacy A. Castner

Department of Psychiatry, Yale University School of MedicineVA Connecticut Healthcare System, West Haven, CT

Critical Factors in Cognition

An internal representation is guiding behavior

There is a model pertaining to relevant events and the demands of the situation

Data is held in an abstract form that can be translated

Response decisions are guided by motivation

Internally guided behavior: Precept vs Percept Expectations in the environment vs ability to change the environment

Choosing optimum goals and deciding relevant events and outcomes

Attending to relevant stimuli and biasing against other environmental events Holding on to key information while relevant and holding back from responding to non-goal-selective

stimuli

Motivation to maintain goal and test behavioral hypothesis

Monitoring outcome and adjusting behavioral hypothesis vs holding fast to a predetermined rule

Working Memory: A Core Cognitive Function Affected in Many Neuropsychiatric Disorders

Working memory: the ability to hold information transiently in mind and process it to use later. Maintenance vs. manipulation?

Patients with schizophrenia and their unaffected siblings are impaired across a variety of paradigms (Park et al., 1999). How is spatial working memory tested?

Working memory performance is the best predictor of propensity for relapse and social reintegration. How far is this true? Is the dependent on the way in which it is tested?

Working memory deficits are also prevalent in other disorders such as PD, Alzheimer’s and normal aging. Does this mean there is no specificity of working memory deficits to schizophrenia?

What is Spatial Delayed Response?

Attend to a spatial sensory stimulus

Maintain goal of acquiring preferred food treat

Understand the basic limitations and provisions of the task (only one choice, only limited time) Remember target location (e.g., where well was baited vs. where to respond)

Motivation to remember target location

Overcoming distraction

6-OHDA Dopamine Depletion in Primate dlPFC Impairs Working Memory

Control

DA-Depletion

Ablation

Adapted from Brozoski et al. Sci.1979 205:929-932

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Spatial Delayed Response

Measure: Improvement of performance from stable baseline of mean = 65 -75% correct and SEM ≤2.5% over 10 – 20 test sessions

Ketamine Profoundly Impairs Working Memory

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F[3,36] = 11.852; p = 1.51E-05. * Significantly differs from placebo (p < 0.05)

Roberts et al. Psychopharmacol 2010

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Overall ANOVA: F[3,36]=6.266; p = 0.002. Significant post hoc comparisons for 0.0001 and 0.001 mg/kg + ketamine compared to placebo/ketamine (p = 0.003 and 0.039 respectively); 0.00001 mg/kg + Ketamine is not significant compared to placebo/ketamine (p = 0.393)

Linear, F[1,36] = 2.876; p = 0.099

Quadratic, F[1,36] = 14.036; p = 0.001

Dose-dependency of the Full D1 Agonist Shows an Inverted-U Function

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Roberts et al. Psychopharmacol 2010

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with the GlyT1 Inhibitor PF3463275

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PF3463275 (mg/kg)

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Significant main effects of PF3463275 (F[3, 21] = 6.437; p = 0.003) and ketamine (F[1, 7] = 47.469; p < 0.001); Significant interaction (F[3, 21] = 9.534); * indicates significance vs. placebo/ketamine by Scheffe post-hoc comparison (p = 0.047 for low dose; p = 0.001 for mid and high doses)

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Oculomotor Delayed Response Tasks

What is different about oculomotor testing?

Stimuli are discrete, with only one visible at a time

Fixation control keeps spatial measures parametric and prevents position/gaze biasing

Many more trials can be performed (sometimes 500 – 1000 in one session)

Lack of interference from other stimuli in mnemonic tasks

Allows for many task alternatives, including antisaccade and control tasks such as those requiring visually guided saccades

Gives measures not only of correct responses but also reaction time and accuracy

Prefrontal Circuitry in Spatial Working Memory

Neurobiological Constructs in Spatial Working Memory

Cellular basis hinges on recurrent excitation and persistent activity. Inhibition and synchronization are required

Prime circuitry involves dlPFC, posterior parietal cortex LIP, and anterior cingulate cortex. Subcortical structures involve striatum and MD thalamus

Performance has shown to be dependent on dopamine signaling by a number of different measures

Functional requirements depend on working memory load. Sensory information is encoded

Functional imaging of D1 agonist reversal of ketamine induced cognitive deficits in the nonhuman primate as shown by regional cerebral glucose metabolism

FDG-PET Methods

Preparation: The study was performed on 8 young adult rhesus macaques that were pretrained to stable performance (65 – 75% 2.5% correct over 20 trials in 20 test sessions) on a standard spatial delayed response task. Animals were required to work for 15 – 25 min, often using highly preferred treats.

Experimental design: A pseudorandom Latin squares design for D1 agonist (A77636) and placebo (sterile water) pretreatments vs. ketamine and placebo (sterile saline) treatments prior to FDG injection and cognitive testing.

Delayed response

Chairing

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Placebo/ketamine – Placebo/placebo contrast

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Effect of Ketamine on rCMGlu in Relation to PFC

Ketamine (1.0 mg/kg IM; 1.7mg/kg in one animal) as compared to placebo, produced an elevation of glucose metabolism in multiple brain regions, including infralimbic/prelimbic cortices, dlPFC Areas 46/8a, and anterior cingulate cortex in the frontal lobes, as well as large areas of parietal cortex and posterior cingulate cortex.

Williams et al. Soc NeurosciAbstr (2008); manuscript in preparation

Interaction of A77636 (0.0001 mg/kg) and Ketamine: PFC

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The high dose of A77636 provided a greater protection from ketamine’s ability to elevate rCMGlu not only in Area 46 but also in parietal cortex.

Williams et al. Soc NeurosciAbstr (2008); manuscript in preparation

Is There an Ideal Spatial Working Memory Task?

How well does it parametize what is being remembered?

How consistent is the attentional component and attentional load

How well is distraction quantified?

What is the precise metric measured and how informative is it of the efficiency of the neural systems involved?

Target locations: Spatial Working Memory with Intervening Stimuli

20°

16°12°

A single trial with four intervening stimuliA single trial with four intervening stimuli

The Space – Color Translocation Task

Attentional Set-Shifting Recruits Homologous Regions of Prefrontal Cortex in Human and Nonhuman Primates

Nakahara et al. (2002) Science 295(5559): 1532-1536

Translational Approaches in Cognition: Sim-GMLT

Development in Collaboration with Dr. Peter Snyder (then of PGRD) and D. Holden of Forza-Bassett

Attention is almost obligatorily measured by reaction time and very dependent upon detection. Competing for attention is a critical construct, where at any time stimuli can be picked out and responded to

Thus, an alternative way to view attention is by having multiple potential stimuli to respond to rather than utilizing particular distracting stimuli. If the outcome for responding to certain stimulus is better than that for others, performance can be measured as total yield over time or propensity to choose high value stimuli

For working memory, attention may be a vital factor for establishing and maintaining sufficient neural representation

For executive function, it can be hypothesized that a model is constructed which predicts outcomes dependent on what is being attended to

From Attention to Executive Function

Cognition utilizes a model of potential salient events and outcomes related to responses. This model guides attention and biases against processing/storage of non-salient events

It is not necessarily just sensory information that is being represented by neural activity but also precepts that are part of the model. Thus, “working-memory buffers” and “executive function” may occupy much of the same circuitry

Multiple choice tasks optimize the potential for observing effects of “competing” or “distracting” stimuli

For assessment of working memory, we need to understand how far translation (e.g., space to color) and abstraction of information is involved rather than just “delay” or “intervening stimuli”

Construction Towards Understanding Deficit States