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Summary Chapter 3
Chapter 3 lecture notes Erik Scherder
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Summary chapter 3 + lecturenotes
Various subtypes of dementa exist and they are ofen classifed as cortcal or sub-cortcall D is a
cortcal dementa due to damag e seen to hippocampus in early stag e of the diseasel Vascular
dementa is a subcortcal dementaa because of the defcit in vasculariaaton of subcortcal brain areas
(elg l BG)l The most prevalent type is a subcortcal ischemic vascular dementa ((SVD)l owevera both
forms of dementa are not limited to cortcal and subcortcal areas respectvelya which makes this
classifcaton somewhat arbitraryl murthermorea the formaton of functonal circuits relies on close
collaboraton between cortcal and subcortcal reg ionsa which means that a lesion anywhere in a
circuit will neg atvely aaect that whole circuitl The locaton of the primary lesion matersa howevera
from a NP point of view:
Episodic memory Sn case of a cortcal lesiona the patent will not be able to encode and/or store
the informaton in memoryl ctve recall and recog niton of word lists afer a delay will be badl This
memory defcit is ofen called amnesial Patents with subcortcal lesions are beter able to encode
the wordsa but they have difcultes retrieving the stored informaton from memoryl Thusa actve
recall will be bada but word recog niton will be much beterl This memory defcit is best described as
forgetfulnessl
Lang uag e and speech lang uag e disturbances are characteristc in patents with cortcal lesionsl
Two distnct functonal networks for motor speech producton: (1) preparatory network
(mediofrontal cortexa insula and cerebellum) and an (2) executve network (BGa thalamusa cerebellum
and motor cortex)l Therefore both a lesion in cortcal areas or subcortcal lang uag e areas may
produce lang uag e problemsl
Gross motor actvity basic motor actvity is reg ulated by subcortcal motor areasl The striatum
(sub-cortcal) may become aaected in later stag es of D and may cause Parkinsonian symptoms such
as rig idityl owevera also the primary motor cortex is important as well and is also aaected in Dl Sn
later stag es of Da g ross motor disturbances may occurl
Behavioral and personality chang es depression as a ‘subcortcal’ disorder is characteriaed by
clinical symptoms as anhedoniaa apathya slowness in thinking and motor actvitya forg eeulness
(recog niton > actve recall) and a stooped posturel
Deg eneraton of the basal forebrain cholinerg ic system is seen in a variety of neurodeg eneratve
disordersl This implies the structure has a central role in brain functoning l The system exists of a
g roup neurons that play an important role in the ascending retcular actvaton system ( R ()l St
orig inates from the basal forebrainl Cholinerg ic pathways g o from the pedunculopontne teg mental
nucleus (PPTN) in brainstem to the thalamusa from the septum to the hippocampusa and from the
nucleus basalis of Meynert (NBM) to the amyg dala and other cortcal areasl The basal forebrain /
cholinerg ic system plays a central role in the cooperaton between brainstem areas and brain areas
such as the PmCa striatuma and hippocampus which are involved in hig her cog nitve processesl The
dorsal raphe nucleus (DRN) g ives rise to the serotonerg ic system and the locus coeruleus (LC) to the
noradrenerg ic neurotransmiter systeml
munctonal circuits may have a specifc or g eneral rolea or bothl The R ( plays a more g lobal role in
contributng the functoning of the CN(l The level of g lobal brain actvity (arousal) is controlled by the
R (l reas within the brainstem level play an essental role in the R (a especially the LCa DRN and
PPTN described earlierl Both noradrenerg ic and serotonerg ic systems are most actve while person is
awakel The noradrenerg ic system actvates and the serotonerg ic one inhibitsl The serotonerg ic
system prevents over-arousal from the noradrenerg ic systeml balance between the two systems is
necessary to maintain a balanced level of arousall The LC and DRN project to the NBM in the
forebrainl mrom there the cortcal cholinerg ic system orig inatesl The NBM/cholinerg ic systems has
been considered to be a contnuaton of the R (a due to its mediatng role and diause projectons
, to the neocortex and hippocampusl NBM neurons play an important role in g eneral aspects of
atenton and arousall The LC and DRN tog ether with the PPTN subsequuently project to the PmCl
Throug h the feedback system with descending infuence on LCa DRN and PPTNa the rig ht PmC in
partcular plays a crucial role in suppressing irrelevant stmulil This enables one to focus atenton on
relevant informatona thereby enhancing Emsl
Next to these g eneral networksa there are also some specifc functonal circuitsl These consist of both
subcortcal as well as periventricular white mater pathwaysl They serve to carry out communicaton
between cortcal areas and in doing so they facilitate a variety of complex cog nitve capacitesl
Neuropatholog y that aaects white mater pathways also aaects the capacites of these functonal
circuits:
mrontocerebellar circuit: strong connectons between cortcal and subcortcal reg ionss; from
the PmC to the anterior cing ulate cortex ( CC) to the cerebelluml The circuit plays a role in Em
and is responsible for maximiaing its processing speedl Lesions result in slower processing a
aaectng atentonal capacites as welll (hifing atenton and divided atenton are in
partcular difcultl (ince Ems and atenton are necessary for episodic memorya this circuit is
also important for episodic memoryl murthermorea it is responsible for g ait and motor-
related functons such as tming a balancea motor and postural controla and the preparaton +
executon of movementsl The medial cerebellum is connected to the primary motor cortexa
premotor and supplementary motor cortcesl The lateral cerebellum is connected to the
inferior frontal g yrus and the DLPmCl mirst-in last out principle applied: order of maturaton is
the reversed order of deg eneratonl
mrontostratal circuit: multple white mater tracts connectng cortcal and subcortcal
reg ionsl The PmC works closely with subcortcal areas such as the striatuml The striatum is
composed of the caudate nuclei and putamenl The striatum is part of the BG and sends
strong aaerent projectons to PmC and hippocampusl The circuit is innervated by the
dopaminerg ic systema which orig inates in the substanta nig ral The frontostratal is
responsible for maintenance of Ems and episodic memoryl Damag e will result in atentonal
problemsa memory impairments and a dysfuncton in actvity levelsl There are also bundles
connectng the motor areas with the striatum (g ait and balance control + initatng motor
actvity)l
mrontohippocampal circuit: strong connectons from the hippocampus throug h the
entorhinal cortex (EC) and into the PmCl Cooperaton between hippocampus and PmC
contributes to atenton and memory capacites and plays a role in Ems (because of
involvement of PmC)l Damag e results in memory dysfunctons (most ofen episodic and
working memory)l
Nig rostriatal circuit: orig inates in substanta nig ra ((N)a connects with the striatum and
extends bi-directonallyl mrom (N dopaminerg ic projectons to PmCa targ etng to innervate
that reg ionl mrom (N the circuit extends laterallya projectng dopamine to hippocampusl
(ystem involved in facilitatng smooth movementl Lesions in the circuit may lead to pseudo /
Parkinsonian symptoms (ilela bradykinesia)l
ippoparietal circuit: strong connectons from hippocampus to parietal cortexl St is vital in
integ raton of various sensory inputs and thereby facilitatng various Ems such as working
memory and visuospatal functonsl Lesions result in various forms of memory dysfunctons
and problems with understanding /remembering visual stmulil
(uperior long itudinal fasciculus ((Lm): the (Lm connects the frontal with the parietala temporal
and occipital lobesl The (Lm is responsible for several g ait and motor-related functons such
as imag inaton of g ait and foot movementsa inhibitory motor controla and preparaton of
voluntary movementsl Deg eneraton may lead to a decline in working memorya visuospatal
atenton and selectve atenton among othersl
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