Table Neuroanatomic Distinctions in Memory ...

Present Absent Retrograde declarative memoryb

Insight ConfabuIation Deficits

c

Retrograde

Present

Absent

Infarction of thalamic arteries, trauma, diencephalic tumor, Wernicke-Korsakoff syndrome

Location. Diencephalic

Retrograded contextual memorye

Often present

Often absent

Cerebrovascular accident, tumor, surgery, anterior communicating artery aneurysm

Frontal

"Extent depends on the extent of the damage to the lateral temporal neocortex. bDeficitsin the conscious recall of facts. 'Often caused by deficits in the initial processing stages of memory and sensitivity to proactive interference. dThe degree of retrograde amnesia is variable and is often attributable to attentional deficits that adversely affect encoding and retrieval. Recognition of previously learned material is often normal, suggesting that consolidation is relatively intact. 'Memory for temporal and spatial aspects of events.

a

Anoxia, limbic encephalitis, cerebrovascular accident, Alzheimer's disease

Medial temporal Cause

-

Table 1. Neuroanatomic Distinctions in Memory Impairment

"

$

9

I

'

'

434 O'Connor and Mosin

other factors that contribute to apparent distinctions among amnesic subgroups (Weiskrantz, 1985). In addition, questions have been raised as to whether these groups are neuroanatomically discrete: It may be that patients with medial temporal and diencephalic amnesia share common sites of neuropathology. Furthermore, it is important to note that comparisons across subtypes of amnesia are influenced by extraneous factors such as baseline intelligence, capacity for attention, and prior education. Many studies of diencephalic amnesia have been confined to patients liith WKS (who have less formal education and extensive histories of alcohol abuse), whereas those with MTL amnesia are often of higher premorbid intelligence and socio-

A. The Neuroanatomy of Memory Current information regarding brain systems involved in memory is based on lesion studies with humans and animals. Declarative memory deficits have been associated with damage in bilateral medial temporal brain regions (Scoville & Milner, 1957). Initial investigations with nonhuman primates supported the idea that new learning was dependent on two neural fornix, manlmillary bodies, mammillothala~nictract, and cinp l a t e cortex) and the aniygdaloid pathway (i.e., the amygdala, dorsal medial thalamus, and orbital frontal cortex). Dam-

1

severe amnesia. In a series of articles, Zola-Morgan and colleagues underscored the hippocampus proper, parahippocampal gyrus, and entorhinal and perirhinal cortices as critical substrates for new learning (Zola-Morgan, Squire, Amaral, & SuauM, 1989).Converging data from studies with patients and with nonhuman primates have suggested that damage restricted to the llippocanlpus proper is associated with mild-to-

Amnesic Syndromes 435

moderate memory deficits, whereas damage to the hippocampus and adjacent (entorhinal and parahippocampal) cortices results in severe amnesia. In all likelihood, medial temporal lobe and medial thalamic structures work in concert with one another in establishing new memories. Studies of patients with WXS and other memory disorders secondary to damage in the region of the third ventricle have highlighted the contribution of diencephalic structures in memory. Postmortem analyses have shown that damage to midline thalamic (i.e., the internal medullary lamina and anteromedial ur dorsomedial nuclei) and mam~~lillary nuclei is associated with severe amnesia (Cramon, Hebel, & Schuri, 1985; Markowitsch, 1988). The basal forebrain, including the medial septal nucleus, the diagonal band of Broca, and the nucleus basalis of Meynert, has also been studied extensively in human and animal models of amnesia. The amnesias associated with PR4D and with mpture and surgical repair of ACoA aneurysms have been viewed as by-products of basal forebrain damage. Some investigators have emphasized that damage restricted to the basal forebrain produces mild memory problems, whereas damage to basal forebrain and striatal brain regions produces severe amnesia (Irle, Wowra, Kunert, Hampl, 8 Kunze, 1992). Other investigators have emphasized that septal damage is the cause of true amnesia in basal forebrain lesions owing to the disruption of anatomic connections to the hippocampus (Zola-Morgan & Squire, 1993). There is a great deal of support for the idea that medial temporal lobe and medial diencephalic structures play critical but temporary roles in new learning. Observations of intact remote memory within the context of severe amnesia have suggested that information eventually becomes independent of hippocampal and diencephalic circuitry (Squire, 1994). In their analysis of the literature, Squire and colleagues concluded that the extent of neocortical damage influences severit).of remote memory loss: Limited damage to core hippocampal regions is associated with an attenuated retrograde amnesia, whereas more severe damage in neocortical brain regions may result in extreme retrograde amnesia.

B. Diseases That Give Rise to Amnesia Amnesia occurs in conjunction with a variety of psychiatric and neurological disorders. Owing to space limitations, psychiatric

438 O'Connor ana Mcr'n

addirion, some irlvest.gators have described parienrs rz7:th m a n or!. dchcits in [lie wake of unili~reral primarily left) 1'(3.\ fnfarcr i o ~ i(Hensoil, Marsden, h \:cadorvs, 1974; Utt 1;: Saver. 19'93). IJrlfortunately, many inres~igatorshave failed to inclucie riicasures o f nonverbal nienlory a n d rate of forgetring in their Je,criprion of P(::l-related amnesia. (:or~sequentl!,, it is ciifticult to dctcrm~rie~ ~ h c t l ithe c r memory deficits of par:tnts ivitil unilateral I'(3A illiarction arc qualitarivcl!. or quantitarively dificrent i r o ~ nthose or other amnesics. 11 is importanr ro note that deficits bcyond rncmory loss, including visual field deficit\, hcmiarlopic alexia, pure alcxia, color agnosia, a n d object agnosia, oftcn occur in ;issociation \villi I)(:.\ srrokes. The latter tliffi(.u.ties arc more liiely rzher~rhe lesion extends posterior.). to include occipitc>temporal cortices. Lesions in the posterior parahippocam;>us or collateral isthmcs (a pathrvay connecring rile posrcrior ~)aral~il)l~ocampus lo the association corres) are vierzed ;IS criric;il in the rncriior\, disturbarce in this parient group rCriunon el al., 1985). ;\rlother va5cutar ci7cnt associarcd wirh 1ne1110r\,l ~ i is \ infarction of rhalamic arteries parricularly rhe ruberothalarr~ic an(! paramedian vessels. There is some variability in neurops\,chological protiles related ro locarion oi Ie,ion. .Again,a nuntbcr of cases nave beer1 described wirh ~nernor!, loss secondary to unil;ireral dan~age. 6. WLHNICKE-KORS.AKOFF SYNDROME Fatielits with Wern~ckc-Xorsakoff sync!rome devclop alnriesla as a result of chroriic alcohol abuse and rhiamine debcicncy [L'ictor .&darns,h Col1ir.s. 198'1,. In thc IVcrnicke phase, p l ~ t i e r ~ c1ernonsrr;ttz rs oculornotor p a l s i ~ s ,atirxla, a n d corifusion. 'l'he Kor,akoftia~ip h a l t o i WKS is accompanied by se\.cre n:emory detic irs and pcrs:)nalitv charlge. I'arients wirh \VK5 are prone ro irriral~illtyi ~ r ~aparhy, il problcn~st h i t oitcn underrninc performance o n rasks o i new 1earnir.g (Hurters (;r C e r ~ n a k , Ii)80,. The ncuropathology o r IVKS involves damage in iilllero~nediai,dors~niedial,and intralarninar rlialair.ic nuclei; rnammillary Ixxilcs. ant1 frorltal nerr\,ork systcms [L'ic.tor ct al., 1989r. 'l'he extent t o n.hich rhese arcas scpararely dr coriverger~rlyrehult in anlnesla i\contro\.crsial. Frontal ii.c., executive) defic'its also u r l d c r r n ~ r ~\\'KS e ~ ~ a t ~ e nability t s ' ro learn new jr~iornlarion.It i, irnporra~itrn rlr~dcrsta:idthat thtbtcvere hI(.ohol abuse as\oci;~tc.dtvith LYKS is oiteri accornpanicbd by longstarirlilip 5ocisl isolatior~; ~ n (al gcncral Inch of intcrelt ill rzorld e\.rnt$. 'l'1it.s~prt~norbitlpsycL~o,ocial patterns ad\.crsel!. affcct

Arrnes~cSynuromes 439 WKS patients' performance on tests m c a s u r i ~ gknorzlccige of public events. 7. RUPTURE AND SURGI(:AI. REI'AIR OF .L\CO,\ r\pproximatcly 10Yn of patients rvho surfer r ~ p t u r ea n d undergo surgical repair of alitc'rior c o r ~ i ~ n u r ~ i c a artcr!. ri~~g aneurysn~spreser-t with inemor)' and other beha17iorprobleriis !Stenhouse, Knight, L.ongn~ore,& I(isli;~ra,1991). r)cscriptions of parients rzitll .\CO,\ emphasize amnesia, apathy, disorientat i o r , and confabulation; rhese syrnptoms tnsy be rclated to a nurnbcr of factors including subarachnoicl helriorrh;~ge, \?asospasm, Iicmatoma formation, herniation o i t h e medial tcntpor;il lobes, hydrocephal~rs,and surgical inrcrvention. Ilererogcrleity in the neurops~~chologic.al prcsenrarions of these patients is in all likelihood clue ro the fact that there is trariability in the site of neural cla~nagc.Brain lesions are seen i!i the basal forebrain and striatal and frontal arcah. It is rzidely a5sumcd [hat basal forebrain damage is the crirical underpinning of rhc memory deficits in tliis parielit group, although recent work has suggested that co~nbinedbasal forebrain anc! srriatal lesions may be necessary for severe melnoqr problems to result (Irk ct al., 1992). l'atients with .ACo,l are often described as suffcrir~gfrom atrenrionally based m e ~ ~ i o rproblen~s. y 'fliey tend to benefit irorrl rccogriilion cues, ~ ~ e r h aowirlg ps to proble~nsin the stratcgic search o i mcnlory. .A subgroup of these patients, particu1ar.y rhosc with frontal damage, art. prone t o coniabularion a n d tiirni~~islieci insight. I'crforrnancc on task3 o f Kr\ varie5. In a recent s t ~ ~ dwe y , found that paticnrs with .\Coil demonstrared a temporally grzded R.A o n some test,, whereas their perfornlailce on the other tests of rclnotc merilory was similar to that o f normal cor~trols (O'Connor, \Yalbridge, D'tsposito, McGlinche!,-l(errotli, & .\le.u~ider,1995).

111. NEUROPSYCHOLOGICAL EVALUATION Evaluation of amnesia takes place wirhin the context of a conipreher1sit.e ascrssmcnt of intelligence, attcl~t:sn,language, perception, reasoning, and e~riotionalstatus. Inforlr~ationrtgarding performance across a broad array of neuropsychological tasks is important for diagnostic a n d therapeuric pcrposcLs. L)iagnosis of focrrl an~nesiacannot he made unless it is firmly tstab:ished that the individual is rclarl\rely intact in other cognirive spherts. Information regarding ba,tblirle 1 0 a n d other

440 O'Cunnor and Mur n

cognirire functions faciliratcs rile cteterrni:iation o i the extent a n d w v e r ~ t yof the memory impairment. In a d d i ~ i o n ;I, c o n prehensive neurops\,chological evaluarion clucidares iacrors that adversel!, affect !ncmory ie.g., coexisting depression) ;IS wel! as strengrhs that should be highlighred in remcdiarion The clinic;~lassessmenr of memory ha, been greatly influenccd by c o g r ~ t i v eresearch with a ~ n n e s i cpatients. I:or a period o i time researcliers cniplias.7.cd t h i ~ ramnesia was the result of d i s r u p t i o ~ ~ins xrarrous stages oi learning. On the basis of rhcir work with WKS patients Suttcrs and Ccr~nak(1980) emphasized e n c o d i n g defic~tsas t h e critical problern in arnne\ia. Tnvestigations of HXi. led hfilner and colleagues to s[)cculate tliilt amnesia rv;~sd u e to a n in;~bilityro transier inforination from 5hort- to long-rer~nn?elnory, thereb!. highlighring consolidation deficits in amnecia (Milner, 19b6). \trarringron and Weiskrantz (1968, 19?0! proposed rhiit anlnesia was d u e ro faulty retrieval. \fore recent theorre< regarding iniorn~ation procwsing in z~~nnesia e~nphasizethe in:crdepcndencc amon2 these st;lges (see Cer~nnk,I9s.5, for a revic:~of rhis c,~bjcct). Ikspite t h e fact that researchers n o longer view amnesia x a unit;~rydeficit in a specific stage o i learning, rhc clinical asses?tnent o f amnesia still involves t h e ctiscriminarion between encoding, consclidarlon, and retrieval. I'ersistent use or' the stage rnodel approach in the clinical as