Memory disorders in children - uliege.be€¦ · At the same time, short-term memory disorders are. p0040 most often observed in association withbroadercogni-tive impairment. Children

c0135 Chapter 27

Memory disorders in children

STEVE MAJERUS1, 2* AND MARTIAL VAN DER LINDEN1, 3

1Department of Psychology — Cognition & Behavior, University of Li�ge, Li�ge, Belgium2Fonds de la Recherche Scientifique — FNRS, Brussels, Belgium

3University of Geneva, Geneva, Switzerland

s0005 THEDIFFERENTMEMORYSYSTEMS

p0005 Memory impairments are observed in a broad range ofchildhood disorders, either related to direct brain insult(traumatic brain injury, cerebrovascular accident) or togenetic anomalies leading to alterations of brain develop-ment. Although different theoretical frameworks ofmemory functions currently coexist, there is agreementon the existence of at least four different memory sys-tems. Rarely a child will present impairment in all of thesesystems at the same time. Hence, for efficient diagnosisand treatment, the identification of impaired as well aspreserved memory functions is of utmost importance.

p0010 A first memory function is short-term memory(working memory, immediate memory, primary mem-ory) which holds currently perceived or retrieved infor-mation in an active and conscious format during thecompletion of a cognitive task (e.g., maintaining an un-familiar telephone number one has just looked up in thephone book, for the time needed to dial the number;maintaining a new melody or a new word one has justheard for immediate repetition; maintaining the succes-sive results of an arithmetic problem during mental cal-culation; maintaining the picture of an unfamiliar objectone is copying). Short-term memory allows us to inte-grate current information with the immediate past andthe immediate future and hence is a critical functionfor maintaining internal thoughts and activated cogni-tive representations synchronized with ongoing externalevents. Traditionally, verbal and visuospatial short-termmemory subsystems are distinguished although currentresearch suggests that both systems rely on common at-tentional processes which interact with distinct represen-tational bases (language representations for verbal

short-term memory, visuospatial representations forvisuospatial short-term memory) (Majerus et al., 2010).A further function of short-term memory is to mani-pulate and transform currently maintained information(i.e., working memory) and as such is also stronglyrelated to executive functions and attention.

p0015A second system is episodic long-term memory allow-ing the encoding, storage, and retrieval of information as-sociated with the precise spatiotemporal context in whichthe information was experienced (e.g., rememberingone’s last birthday party, remembering the day whenone was awarded his/her high school diploma, remember-ing the holidays spent in Norway last year, rememberingthe phone call received 10 minutes ago). As such, episodicmemory is intimately related to autobiographicalmemoryand the construction of one’s identity as an individualwitha history of personal events. Episodic memory also has afuture-oriented function by enabling us to think of futureevents (the tasks-to-do today, tomorrow;medical and pro-fessional appointments; planned meetings with friends).

p0020Another long-termmemory system is semantic mem-ory storing general knowledge, scripts, and facts aboutthe world (e.g., What is a dog? What is a house? What dowe do at a restaurant? Which is the capital of Belgium?Why is it cold during winter?). Contrary to episodic long-termmemory, no precise contextual information is asso-ciated with semantic memories: we simply know thatBrussels is the capital of Belgium, even if we do notknow where and when we learned this information. Re-trieval in semantic memory is usually fast and easy,while it is slower and effortful in episodic memory. Se-mantic memory is also a contributor to autobiographicalmemory, by storing self-relevant but decontextualized

Comp. by: pdjeapradaban Stage: Revises1 Chapter No.: 27 Title Name: HCNDate:7/2/13 Time:11:31:03 Page Number: 1

*Correspondence to: Dr. Steve Majerus, Department of Psychology – Cognition & Behavior, Universite de Liege, Boulevard du

Rectorat, B33, 4000 Liege, Belgium. Tel: þ32 4 3664656, E-mail: [email protected]

Handbook of Clinical Neurology, Vol. 111 (3rd series)Pediatric Neurology Part IO. Dulac, M. Lassonde and H.B. Sarnat, Editors© 2013 Elsevier B.V. All rights reserved

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knowledge such as the date one was born, one’s nation-ality, the names of close relatives. Semantic memoriesare often acquired implicitly, but they can be retrievedexplicitly while episodic memories are acquired and re-trieved explicitly.

p0025 Finally, procedural long-term memory is a relativelyheterogeneous concept broadly regrouping complexsensorimotor knowledge and skills that are acquiredimplicitly or explicitly and, once fully automatized, aredifficult to verbalize (e.g., skilled reading, speaking,writing, advanced music playing, running a cycle, skilledtyping on a computer keyboard).

s0010 SHORT-TERMMEMORYDISORDERS

p0030 Impaired short-term memory is reflected by a reducedability to temporarily store and reproduce verbal and/orvisuospatial information that has just been presented.Children with impaired verbal short-term memory willthus show poor ability in the immediate reproduction ofverbal sequences (e.g., lists of digits, words or unfamil-iar words) and/or visuospatial patterns (e.g., objectcopying, spatial sequence reproduction). Given the im-portance of short-term memory as a first step towardlong-term learning of new information, these childrenwill typically also have difficulties in learning newverbal information such as a new vocabulary, newdefinitions, and in learning associations betweenabstract concepts as for example needed in chemistry(Baddeley et al., 1998). Furthermore given the implica-tion of short-term memory during mental calculationand reasoning, difficulties will also be observed in ar-ithmetic and sentence comprehension. The deficit canbe selective for verbal or visual information, or involveboth modalities. Although short-term memory deficitsdo not prevent successful completion of primary andsecondary school education, they will neverthelesscause a significant handicap by slowing the affectedchild’s learning rate and his/her comprehension ofthe explanations and task assignments provided bythe teaching staff.

p0035 The observation of a selective short-termmemory im-pairment, in the absence of any other cognitive deficit, isextremely rare. This is partly due to the fact that short-term memory deficits are the consequence of lesions inthe inferior parietal lobule and/or the inferior frontal gy-rus, most often as a result of a cerebrovascular accidentin the territory of the left middle cerebral artery. Thiskind of accident is rare in children. Furthermore, trau-matic brain injury, more common in populations of chil-dren, rarely leads to focal and selective lesions in theseareas, although short-term memory disorders are a fre-quent consequence of traumatic brain injury in associa-tion with other memory impairments (episodic memory).

Three cases have been described presenting a selectiveverbal short-term memory disorder in the absence ofany documented brain insult, but with the predicted ac-companying difficulties in learning new verbal informa-tion (Baddeley, 1993; Baddeley andWilson, 1993; Hantenand Martin, 2001). However, at least for two of thesecases, more general language impairment could not becompletely excluded.

p0040At the same time, short-term memory disorders aremost often observed in association with broader cogni-tive impairment. Children with specific language im-pairment and children with dyslexia typically showpoor verbal short-term memory and working memoryspans; the reduction in verbal short-term memory inthese populations cannot be fully explained by theirpoor language abilities, and hence it is likely thatthe short-term memory deficits further contribute tothe already protracted language development in thesechildren. More generally, verbal short-term memorydeficits are a residual deficit in many populations whichinitially presented more global language impairmentpatients who presented specific language impairment,childhood aphasia, or epileptic childhood aphasia(Landau-Kleffner syndrome) during childhood canshow relatively good language recovery at adulthoodbut verbal short-term memory impairment will still bepresent (Majerus et al., 2004).

p0045A number of genetic syndromes are also character-ized by poor short-term memory spans, either for verbalshort-termmemory, such as in Down syndrome (trisomy21) or for visual short-term memory, such as inWilliams syndrome (7q11.23) and X-related syndromes(Fragile X, Turner syndrome, Klinefelter syndrome,and Rett syndrome). Velo-cardio-facial syndrome(microdeletion 22q11.21) is particularly interesting heresince a specific deficit for the retention of orderinformation has been observed: affected children can ac-curately maintain and reproduce the items (e.g.,words, digits) that have been presented to them but theywill have more important difficulties in maintainingand reproducing the order in which the items have beenpresented (Majerus et al., 2007). Recent studiessuggest indeed that one of the major functions ofshort-term memory is to maintain the order of eventsthat just occurred, the events themselves being directlycoded via temporary activation of the respective long-term knowledge bases (i.e., the language system for ver-bal information) (Majerus, 2009). Finally, we shouldnote that in Fragile X syndrome, the short-term memoryimpairment is typically more general, including poorretention for verbal, visual, and order information,most likely related to more fundamental attentional dif-ficulties during encoding of information in short-termmemory.


2 S. MAJERUS AND M. VAN DER LINDEN


s0015 EPISODIC LONG-TERMMEMORYDISORDERS

p0050 Children presenting with episodic memory deficits willhave difficulties explicitly learning and/or retrievingnew information and its associated spatiotemporal con-text. These children will forget appointments, tasks-to-do, and activities they had the same day or severaldays/weeks ago. This will also reduce their ability to pro-ject into the future and to design future plans/activities.If therewas an acute onset ofmemory difficulties, mem-ories that have been learned before the onset will gener-ally remain intact and will continue to be retrievedaccurately. Furthermore, the deficit can be characterizedeither by difficulties during encoding (information is notcorrectly encoded in episodic memory), during consoli-dation (high forgetting rate), and/or during retrieval(information cannot be retrieved but if correct retrievalcues are provided, performance can be improved).Although these children will show important difficultiesin remembering everyday activities, learning of semanticand procedural information via repeated exposure isnevertheless possible. Hence these children can evolvein a standard educational setting in a satisfactory man-ner, but episodic aspects of learning will be poor orimpossible.

p0055 A frequent cause of selective episodic memory defi-cits, leading to a pattern of developmental amnesia, arelesions to the bilateral hippocampal areas as a result ofanoxia, ischemia, or carbon monoxyde poisoning. Theselesions will particularly affect the consolidation stage ofepisodic memory. In some cases, recognition memorycan be relatively preserved, as opposed to full, uncuedrecall. If these lesions occur at a very early age (i.e., atthe perinatal stage), the difficulties in episodic memorymay be observable only 3 to 4 years later, when episodicmemory starts to get recruitedmore extensively. In somecases, the episodic memory deficit may be restricted tothe verbal or the visual condition (Temple andRichardson, 2006).

p0060 Other causes leading to episodic memory deficits aretraumatic brain injury (in about 50% of children withtraumatic brain injury), brain tumors (especially those in-volving the third ventricle), and cerebrovascular acci-dents. Epileptic disorders, especially those involvingthe medial temporal lobes, are a further frequent causeof episodic memory deficits. If the epileptic foci areunilateral, the memory deficits may be restricted toverbal (left temporal) or visual (right temporal) informa-tion, although more general deficits are observed whenthe foci are bilateral (Temple, 2002). It is important tonote that even a single status epilepticus can lead toalterations in the hippocampal regions 5 days after onset(Scott et al., 2002).

p0065More subtle and strategic deficits during memoryretrieval have been observed in children presentingwith attention-deficit/hyperactivity disorder (ADHD).Cornoldi and colleagues (1999) observed deficits in 12-year-old children with ADHD in a picture recall taskwhen no information about possible encoding strategieswas given (such as regrouping the pictures according totheir semantic category). However, recall performancewas normalized when the children were informed aboutthe strategy and were trained to use it, indicating that thememory deficits in ADHD are characterized by difficul-ties in implementing accurate encoding and retrievalstrategies, rather than impairment at the level of consol-idation. In the same vein, premature birth is a further riskfactor for developing episodic memory disorders, al-though the impairments may be relatively subtle andnot significant in all children born preterm.

p0070Finally, episodic memory deficits are also observed ina range of genetic disorders such as Rett syndrome, Kli-nefelter syndrome, Down syndrome, velo-cardio-facialsyndrome, and Williams syndrome, the two lattersyndromes being characterized by an impairmentespecially for visual episodic memory.

s0020OTHERMEMORYDISORDERS

p0075Semantic memory disorders will lead to deficient factualknowledge and poor semantic categorization (e.g., Do“cat” and “dog” belong to the same semantic category?),while categorization based on phonological informationwill be possible (e.g., rhyme judgment). Vocabularyknowledgewill also be poor while other language aspectswill be preserved. In children, semantic memory disor-ders are less frequently observed, relative to episodicor short-term memory disorders. They are typically theconsequence of lesions to the medial and lateral inferiortemporal lobe, even in the absence of damage to thehippocampal area (Temple and Richardson, 2006).Although semantic memory disorders have been lessintensively investigated, they appear in children present-ing with late-onset temporal lobe epilepsy, especiallyleft mesial temporal lobe epilepsy, although memory im-pairment is less frequent than it is in adults presentingwith the same type of epilepsy (see also Jambaque &Lassonde, this volume). More generally, impairedsemantic memory characterizes a number of geneticsyndromes associated with mental retardation, such asWilliams syndrome, Down syndrome, and Fragile X.

p0080Finally, difficulties in procedural memory are charac-terized by various difficulties in learning new sensorimo-tor skills, such as those involved in becoming a skilledmusic player, a skilled reader, or a skilled speaker. Thesedifficulties are very rarely observed as a result of acquiredbrain lesion but may occasionally appear during epileptic


MEMORY DISORDERS IN CHILDREN 3


disorders, especially if the cerebellum is involved, as sug-gested by a study in adult epileptic patients (Hermannet al., 2004). On the other hand, genetic syndromes suchas Williams syndrome have been associated with

procedural memory disorders, as tested by serial reactiontime tasks, possibly related to abnormal development ofbasal nuclei which are involved in procedural learning.More generally, the difficulties in learning to speak in


t0005 Table 27.1

Synopsis of memory impairments, associated syndromes, and associated cerebral/genetic anomalies

Memory system Symptoms Syndromes Brain lesions/genetic anomaly

Short-term memory

Verbal Inability to maintain for a fewseconds new verbal

information; difficulties inacquiring a new vocabulary

Developmental STM disorder

TBI, CVA , epilepticsyndromes

Down syndrome

Fragile X

None

L posterior temporal/Linferior frontal

Trisomy 21

Xq27.3 mutation

Order Difficulties in maintaining the

order of events

Velo-cardio-facial syndrome 22q11.2 microdeletion

Visual Inability to maintain for a few

seconds new visualinformation; difficulties inmental imagery

Traumatic brain injury or CVA

Williams syndrome

R parieto-occipital

7q11.23 microdeletion

Fragile XTurner syndromeKlinefelter syndromeRett syndrome

Xq27.3 mutation45X0, 47XXX47XXY, 47XYY, 48XXXYXq28 mutation

Episodic memory Inability to learn newinformation and its

spatiotemporal context;increased forgetting of pastand future events

Developmental amnesia

Mesial temporal lobe epilepsy

Bilateral hippocampi

L and/or R hippocampus

TBI

Brain tumor, CVA

Down syndromeWilliams syndrome

Velo-cardio-facial syndromeKlinefelter syndromeRett syndrome

Dorso-lateral prefrontalcortex; diffuse axonalinjuries

3rd ventricle

21 trisomy7q11.23 microdeletion

22q11.2 microdeletion47XXY, 47XYY, 48XXXYXq28 mutation

Semantic memory Inability to learn factualinformation; poor

vocabulary knowledge

Temporal lobe epilepsy L lateral inferior and medialtemporal lobe

Williams syndrome 7q11.23 microdeletion

Procedural memory Difficulties to learn

sensorimotor skills (speech,reading, music playing,keyboard typing)

Temporal lobe epilepsy

Williams syndromeSpecific language impairment?Dyslexia?

Cerebellar involvement

7q11.23 microdeletionNoneNone

CVA, cerebrovascular accident; STM, short-term memory; TBI, traumatic brain injury; L, left; R, right.

4 S. MAJERUS AND M. VAN DER LINDEN


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specific language impairment and in learning to write indyslexia have been suggested to reflect impairment in pro-cedural memory, preventing the automatization of thecomplex auditory-motor and visual-motor loops involvedin the production of oral and written language, respec-tively (Ullman and Pierpoint, 2005).

s0025 CONCLUSIONS

p0085 This chapter provides an overview of the main memorydisorders encountered in neuropediatric populations(see also Table 27.1). Althoughwe have presented the dif-ferent disorders as separate entities, some of these canco-occur. For example, lesions to the medial temporallobe often lead to both semantic and episodic memorydeficits, depending on the extent of the lesion and the in-volvement or not of hippocampal areas. Similarly, im-pairments in short-term memory and episodic memoryfrequently co-occur in children suffering from trau-matic brain injury. Moreover, the different memory sys-tems interact: although semantic memories can belearned while episodic memory is significantly impaired,a joint intervention of both systems will lead to the fast-est learning rate of new information. Similarly, the codesused in short-term memory tasks are shared with long-term memory systems: semantic information in ashort-termmemory task will be stored by first activatingcorresponding information in long-term semantic mem-ory. Hence, a deficit in one memory system will also im-pact on other memory systems. Future studies will needto determine the precise mechanisms that allow these in-teractions betweenmemory systems and how these inter-actions can be affected via brain pathology.

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MEMORY DISORDERS IN CHILDREN 5


Non-Print Items

ABSTRACT

Memory disorders are a frequent consequence of a variety of childhood neurological conditions. We will review thecharacteristics of memory disorders as a function of the main four memory systems: short-term memory, episodicmemory, semanticmemory, and proceduralmemory. For each system, wewill identify themost typical cerebral and/orgenetic correlates, and we will discuss the impact of impairment of eachmemory system on everyday life functioning.


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Memory disorders in children - uliege.be€¦ · At the same time, short-term memory disorders are. p0040 most often observed in association withbroadercogni-tive impairment. Children