Working Memory: Bridging Cognitive Theory and ...

Working Memory: Bridging Cognitive Theory and Clinical Neuroscience Robert D. Shura, Psy.D. , Robin A. Hurley, M.D. , & Katherine H. Taber, Ph.D. 1-3

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VISN 6 MIRECC Mental Illness Research, Education & Clinical Center

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Sources of support: Mid-Atlantic Mental Illness Research, Education and Clinical Center & W.G. Hefner VAMC 1. Veterans Affairs Mid Atlantic Mental Illness Research, Education and Clinical Center, VISN 6; 2. W.G. Hefner VAMC, Salisbury, NC; 3. Wake Forest School of Medicine; 4. Via College of Osteopathic Medicine 5. Baylor College of Medicine

INTRODUCTION

CENTRAL EXECUTIVE

Memory is complex, and involves multiple processes. Learning describes processes related to acquiring information and skills; memory includes processes related to accessing information and skills. Working memory includes processes that allow for movement of information to and from long term memory storage (explicit/declarative memory), and systems related to mental manipulation. The purpose of this poster is to synthesize research on the cognitive psychology theory, functional neuroanatomy, and clinical relevance of working memory based on the most recent version of the Baddeley Model.

LEARNING Encoding Initial process of acquiring information

MEMORY

Consolidation Process of stabilizing a memory after encoding

This model shows and defines the processes involved in learning and memory. Note too that a piece of information is called a chunk, and can either be a single item or a cluster of items.

Retrieval Process of accessing information from memory

ENVIRONMENTAL INPUT

Capacity: limited

Short Term Stores Duration: 30 sec. Capacity: 5-9 chunks

The Central Executive is the attentional control processing station of working memory, and has been dissociated into independent but related processes that fall under the executive functions. FUNCTIONS Baddeley (1996): Multitasking, retrieval strategy switching, selective inhibition, and mental manipulation. Morris & Jones (1990): Updating and modifying information. Commonly activated brain regions: prefrontal, anterior cingulate, parietal, temporal, and insula cortical areas (Colette & van der Linden, 2002).

Recognition: identify

Long Term Stores Duration: permanent Capacity: infinite

Control Processes Rehearsal, strategies, etc.

Figure based on Atkinson & Shiffrin (1968). Human memory: A proposed system and its control processes.

The Phonological Loop is the working memory system for maintenance and manipulation of auditory-verbal information, and is the most researched aspect of the Baddeley Model. EXAMPLE Verbal repetition (rehearsal) of information needed for a short period of time, such as repeating a phone number over and over until one is able to dial or write the number down. Baldo and Dronkers (2006) compared 10 patients with inferior parietal (IP) lesions, 8 patients with inferior frontal (IF) lesions, and 6 controls on a series of phonological storage (digit span, repetition) and auditory rehearsal (N-Back, rhyming) working memory tasks. IP participants performed significantly worse than controls on phonological storage tests and the N-back, and IF participants were significantly worse than controls on one test of rhyming. This supports the involvement of left fronto-parietal regions in 2 distinct aspects of phonological loop division of working memory. A A: Reconstruction of 10 participants with IP lesions.

RESPONSE OUTPUT

B

The main model of memory prevailing in cognitive psychology in the 1960's was the Atkinson & Shiffrin Model, depicted above. One of the problems with this model was the assumption that information moves from Short Term Memory to Long Term Memory passively, essentially based on time in Short Term Memory. Additionally, there seemed to be some more active process mitigating movement of information between Short Term and Long Term Memory Stores. From neuropsychology, for example, one can have intact ability to recall simple information after 20 seconds, but be impaired on retrieval after long intervals and/or perform poorly when required to manipulate information (such as mental arithmetic). Thus, new models were needed.

BADDELEY’S WORKING MEMORY MODEL

Fluid Systems

Crystallized Systems

INPUT Phonological Loop

Language

B: Reconstruction of 8 participants with IF lesions. Baldo & Dronkers (2006). The role of inferior parietal and inferior frontal cortex in working memory.

A recent study using transcranial direct current stimulation (tDCS) and fMRI found cerebellar-parietal involvement in late encoding of verbal information. The image to the right shows posterior parietal activation following tDCS of the cerebellar lobule VIIb during late encodoing.

Macher, Bohringer, Villringer, & Pleger (2014). Cerebellarparietal connections underpin phonological storage.

VISUO-SPATIAL SKETCHPAD The Visuo-spatial Sketchpad is the working memory system involved in the maintenance and manipulation of visual information. It was initially thought that there was a left-right hemisphere differential activation between the verbal and spatial working memory systems (Jonides et al., 1993). However, additional research suggested bilateral activation in both systems (Cabeza & Nyberg, 2000). EXAMPLE Giving someone directions or describing a famous painting. A

Central Executive

Episodic Buffer

Visuo-spatial Sketchpad

OUTPUT

Episodic LTM

Visual Semantics Based on Baddeley (2000)

The Working Memory Model contains four parts: the Central Executive, Phonological Loop, the Visuo-spatial Sketchpad, and the Episodic Buffer. Each of these four systems are considered separately.

The Episodic Buffer component of working memory was included in working memory years after the other three components were modeled (Baddeley, 2000). The Buffer serves as a work bench on which information from long term memory, the Phonological Loop, and the Visuo-spatial Sketchpad are manipulated in real time, according to the direction of the Central Executive. Thus, the Episodic Buffer is a transitory system by which information is worked, and moves to and from long term storage. ANATOMY It remains unclear where in the brain the Episodic Buffer resides. An fMRI study of 21 Alzheimer’s dementia patients compared to 22 controls suggested involvement of the left anterior hippocampus (Berlingeri et al., 2008). A smaller fMRI study with 5 healthy adults implicated prefrontal, premotor, temporal-parietal junction, and parietal involvement (Zhang et al., 2004). A larger review study (Vilberg & Rugg, 2008) concluded inferior parietal areas might best relate to the Episodic Buffer.

PHONOLOGICAL LOOP

Recall: reproduce

ATKINSON & SHIFFRIN’S MEMORY MODEL Sensory Register Iconic: < 1 sec. Echoic: 2-4 sec. Other (Kinesthetic, etc.)

EPISODIC BUFFER

An fMRI study (n=31) used verbal-based and spatial-based N-Back tests (Ray et al., 2008). Results showed that both the verbal and spatial working memory tasks activated similar bilateral fronto-parietal networks (rows A and B to right). The verbal working memory tasks led to greater activation in the left hemisphere; the spatial working memory task did not show preferential activation (row C to right). This suggests a general working memory system, which both the Visuo-spatial Sketchpad and Phonological Loop activate, but that the Phonological Loop also activates left hemisphere circuitry.

B

CLINICAL A number of different tests are available to neuropsychologists for testing working memory. SPAN TASKS Digit Span: subtest from the Wechsler Adult Intelligent Scales-IV (WAIS-IV). In this test, the patient is read a string of numbers and asked to repeat the numbers as they were read, in reverse order, and in order from lowest to highest. The strings of numbers increases in length. The “Magic 7 plus or minus 2" law states that the average adult can remember 5 to 9 numbers (Milner, 1956).

Below: The Corsi Block. In this task, the examiner touches the blue blocks in a particular order, that the patient is to then repeat back.

Letter-Number Sequencing: letters and numbers are read and both must be placed in order by the patient mentally manipulating the material. Spatial Span: subtest from the Wechsler Memory Scales-IV (WMS-IV), in which a patient must remember the order that the blue blocks are touched on the Corsi Block. MENTAL MANIPULATION Arithmetic: subtest in WAIS-IV. Patient must remember information, determine computation needed, and complete mental calculation. COMPLEX TRACKING N-Back tests: commonly used in research, a clinical variation of which is the Paced Auditory Serial Addition Test (PASAT). In this test, a string of 61 numbers are read, and the patient must add each number to the number immediately proceeding. IMPAIRMENT Importantly, processing speed and basic attention are requisite skills for working memory, thus clinicians must assess a variety of domains to interpret impaired working memory test performance. Poor performance on these tests has been correlated to left hemisphere and frontal injury, and poorer performance has been documented in patients with moderate to severe TBI, Alzheimer’s disease, and schizophrenia (Lezak et al., 2012). Impairing Working Memory An fMRI study of 21 subjects performing a verbal N-Back task evaluated the effects of social evaluative threat on task performance and functional activation (van Ast, 2014). Social threat related to poorer working memory performance and decreased activation in lateral PFC and intraparietal sulcus, as well as decreased connectivity between the two areas.

Enhancing Working Memory A study of 101 adults (Brose et al., 2014) examined the effects of positive affect (PA) on working memory over the course of 120 days. Higher PA was associated with better performance on verbal and spatial working memory tasks, but not numeric. PA was also associated with higher motivation.

CONCLUSIONS C

Ray, Mackay, Harmer, & Crow. (2008). Bilateral generic working memory circuit requires left-lateralized addition for verbal processing.

Working memory was initially described during a zeitgeist when cognitive psychology used computer-based informational models to guide theoretical thought. Since, numerous studies from cognitive psychology, neuropsychology, and neuroimaging have advanced the understanding of working memory within the wider realm of learning and memory. Currently, working memory tasks are frequently used in functional imaging research paradigms (e.g., N-Back), nearly always assessed in clinical neuropsychological evaluations, and generally considered a set of independent but related processes involving many areas of the brain.