Yet he can understand the meaning of
a spoken message. This achievementis
based upon associations which were developed between sensory stimulation
and central patterns of nerve excitation
at an early stage in the learning process. Whenever similar patterns of verbal stimuli are presented, the old memories and the corresponding contents
of consciousness become reactivated
and comprehended. Thus, there is no
trace of a causal evolution of understanding of verbal stimuli by way of
an uninterrupted chain of conscious
correlates of the sensory mechanisms.
Instead, central patterns of excitation
are elicited as though by resonance
when specific sensory messages arrive.
However logical this may sound it does
not explain the process of transformation itself, which seems to be a separate
biological faculty. No road to its understanding seems open at present.
It has been known for a long time
surface
elements
in
the
neighborhood of a dark field appear
lighter than elements that lie away
from the light-dark border. This difference in brightness is felt explicitly
although objective checking shows that
all the light fields are identical in tone.
Therefore, until a short while ago the
so-called simultaneous contrast had
been interpreted as a subjective phenomenon. Recently this contrast effect
was shown to be already manifest in
the neural plane of the visual system
(12). This was something of a sur-
prise. The evidence discloses that contrast phenomena arebasically produced
by collateral inhibition involving neigh-
boring elements at retinal as well as
central levels. The physiological effect
of this mechanism is the sharpening
of the border between light and dark
areas in the visual field. Thus the correspondence between subjective impressions and patterns of neural activity
in the visual system is documented.
A second example of the close interrelationship between function of brain
systems and mental processes is the
well-known fact that consciousness is
lost when critical areas of the brainstem are damaged (23). In contrast,
consciousness remains unaffected when
only parts of the cerebral cortex are
damaged. At most, a limited defect
may result, such as a scotoma of per8 DECEMBER 1967
and time are undisturbed. With this,
proof exists that specific psychic functions are bound to specific nervous
structures. Still, the intervening proc-
ess between stimulation of nervous elements and the formation of a conscious
perception remains beyond our grasp.
A third example concerns the release of definite sensations through artificially induced stimulation of the
brain. One recalls the activation of a
characteristic behavior pattern in ex-
perimental animals (goats) after intra-
diencephalic injection of hypertonic
saline. Their response was a massive
intake of water (/4). This behavioral
reaction is identical to that induced
by long-term deprivation of water. The
is increased, and the thirsty animal is
impelled, as the human is under simi-
and Neural Events
light
the situation and is capable of answering questions intelligently. His selfawareness and his orientation in space
electrolyte concentration in the tissue
Subjective Experience
that
ceptive integration. In spite of this defect, the patient remains conscious of
lar conditions, to quench its thirst by
drinking. The observation implies that
the stimulated area of the brain contains receptors which control osmotic
pressure by regulating the water balance. The immediate impulse is normally given by the specific sensation
of thirst in association with the positively conditioned satisfaction of removing the thirst sensation.
Another example of drive behavior
elicited by stimulation of the diencephalon concerns food intake (/5). Here,
extreme voracity may develop under
the influence of central excitation, resembling that seen after prolonged
fasting or as a consequence of insulin-
induced fall of the blood sugar level.
Such increased intake of food (bulimia)
is also seen in some psychically dis-
turbed human subjects. Thus, physio-
logical hunger, experimentally induced
hyperphagia, and pathological bulimia
to the direct stimulation of efferent
pathways? This is obviously not the
explanation. For, if the experimenter
reaches toward the cat at the climax
of excitment, it strikes at him angrily
in a well-directed attack. At the onset
of stimulation the animal may inspect
the environment and, in its search for
a refuge, may suddenly jump off the
laboratory table and flee to a hiding
place. These observations indicate
strongly that the stimulation, induced
attack, and flight reactions are not purely motor effects; rather, they represent
interactions between highly integrated
central patterns of motivational behavior and conscious visual perceptions
of the environment.
The experiment with goats mentioned
above is even more convincing (16).
In the standard experimental procedure
the animals are first acquainted with
a well-defined source of water. After
being deprived of water for a period
they begin to seek water at this source.
To reach it, they must surmount an
obstruction and climb a ladder. After
many trials the second part of the experiment begins—-namely, electrical
stimulation of specific structures of the
diencephalon when the animal is hydrated. The trained animal uses the ladder promptly, goes directly to the familiar water vessel, and drains it. The
short time between the beginning of
stimulation and the action described
leads to one conclusion: the effect of
electrical stimulation of specific diencephalic structures manifests itself in
the subjective sphere as a drive, thirst.
This drive gives inducement and direc-
tion to the behavior, through which the
tension of drive is relieved. Thus, it
seems appropriate to conclude that, under the influence of brain stimulation,
experiencesstored in the memory are actively integrated with instant perceptions
and released as behavioral responses.
appear interrelated inasmuch as they
may be subserved by identical cerebral
systems.
Another set of observations refers
to manifestation of rage and fear elicited by stimulation of the hypothala-
mus in cats (J5). With the onset of
artificial stimulation the cat begins to
snarl, hiss, and spit. It arches its back
or crouches, it bristles, and it lashes
its tail. Thus, the typical defense reaction develops, as in an animal threatened by an enemy—for example, a cat
threatened by an attacking dog. The
question is raised, Are these effects due
Effects of Psychotropic Drugs
Electrical brain stimulation is not
the only means whereby subjective experiences may beelicited or modified;
they may be influenced considerably
by the action of chemical agents. One
of the best-known examples is the effect of ethyl alcohol. With moderate
doses, the individual’s mood is usually
improved;
he
experiences
an in-
creased desire for adventure, including
an urge for verbal communication. His
euphoria is accompanied. by a’ suppres1281