A.R. Luria The Working Brain p.58-60

Peter F. effectivespamblock at ozemail.com.au
Wed Feb 11 01:29:38 EST 2004


p. 58 Functional Organization and Mental Activity



connections also exist between the cortex and the lower formations:

it is these connections which transmit the regulatory Influence of the

cortex on the lower structures of the brain stem and which are the

mechanism by means of which the functional patterns of excitation

ilrising in the cortex recruit the systems of the reticular formation of

the 'old' brain and receive from them their charge of energy.

The descending structures of the reticular formation have been

investigated much less fully than its ascending connections. However,

a series of studies (French et al., 1955; Segundo et al., 1955;

Galambos and Morgan, 1960; Magoun, 1963; Narikashvili, 1962;

1963; 1968; Adrianov, 1963) has shown that through the inter-

mediary of these cortico-reticular tracts stimulation of individual

areas of the cortex can evoke a generalized arousal reaction (Brazier,

1960; Galambos and Morgan, 1960), facilitate spinal refiexes, modify

the exdtability of muscles through the system of y-afferent fibres,

increase the excitability of the cochlear apparatus (Hemtodez-

Peon et al., 1956; Narikashvili, 1963), and lower the thresholds of

discrinmiatory sensation (Jouvet and Hem4ndez-Pe6n, 1957; Lindsley,

1951; 1958; 1960).

Both morphological and morphysiological investigations have

thus reliably shown that, besides the specific sensory and motor func-

tions which we have already discussed, the cerebral cortex also per forms

non-specific activating functions, that every specific afferent or efferent

fibre is accompanied by a fibre of the non-specific activating system,

and that stimulation of individual areas of the cortex can evoke both

activating and inhibitory influences on lower brain structures (Jouvet,

1961; Buser et at., 1961; Narikashvili, 1963; 1968; Sager, 1968;

Henrindez-Peon, 1966; 1969; Durinyan et al., 1968). It has also been

shown that the descending fibres of the activating (and also of the

inhibitory) reticular system have a well-differentiated cortical

organization. Whereas the most specific bundles of these fibres

(raising or lowering the tone of the sensory or motor systems) arise

from the primary (and, to some extent, the secondary) cortical zones,

the more general activating influences on the reticular formation of

the brain stem arise primarily from the frontal region of the cortex

(French et al., 1955; Segnndo et al., 1955; Nauta, 1964; 1968;

Pribran), 1959b; 1960; 1966a; 1971; Homskaya, 1966b; 1969; 1972;

Sager, 1968) (Figure 10). These descending fibres, running from the





p.59 diagrams

p.60

prefrontal (orbital and medial frontal) cortex to nuclei of the thalamus

and brain stems form a system by means of which the higher levels of

the cortex, participating directly in the formation of intentions and

plans, recruit the lower systems of the reticular formation of the

thalamus and brain stem, thereby modulating their work and making

possible the most complex forms of conscious activity.

The medial zones of the cerebral hemispheres belong, so far as

their origin and structure are concerned, mainly to the paleocortex.

archicortex and mtennediate cortgx (Filimonov, 1949) and they

retain their particularly close connection with the reticular forma-

tions of the brain stem. The older writers united ail these structures

under the common name of rhinencephalon (which subsequent

research has not upheld), but later writers, bearing in mind their

very close connection with the structures of the upper parts of the

brain stem and hypothalamus, and with visceral functions, have

preferred to describe them as the *visceral brain'. Neither of these

appellations is entirely accurate, however, since the most notable

function of these structures involves processes of consciousness and

memory.

Early investigations, starting with the observations of Kluver

(Khiver and Bucy, 1938; Kluver, 1952) and ending with the most

recent observations of Olds (1955-9), MacLean (1952; 1958)

and many others have shown that a lesion of these brain zones in

animals causes marked changes in biochemical processes, leads to

changes in the animal's needs, induces a state of rage, and so on.

These facts clearly show that the principal function of these brain

zones is not ccmmuniccUion with the outside world (the reception and

analysis of information) the programming of actions), but regulation

of the general state, modification of the tone and control over the

inclinations and emotions. In this sense the medial zones of the hemispheres

can be regarded as a system superposed above the structure

of the upper part of the brain stem and reticular formation.

These views have been confirmed by morphological and physio-

logical data. It has been shown, firstly, that the great majority of

neurons in this part of the cortex do not possess any definite modal

specificity, but respond actively to changes in the state of the organ-

ism. Secondly, it has been shown that stimulation of these zones

does not lead to the appearance of differentiated discharges and,

60 Functional Organization and Mental Activity





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