In article <7md2cq$q6l at freenet-news.carleton.ca>, Marek Ghosh
<be206 at FreeNet.Carleton.CA> wrote:
> I have read examples of odd behaviour ranging from subtle to outright
> unacceptable, caused by different neurological causes.
>> Mild strokes, small brain tumours and head injury might cause abberations of
> behaviour.
>> If this is true, are there books which specifically cite a number
> of examples of this type of behavioral change and the precise causes?
>> Would anyone comment on the validity of cause and effect between
> neurological damage and behavioural changes.
A good place to start is with the work of the Damasios in Iowa. They
have catalogued the neuropsychological effects of a large number of
well defined human brain lesions. Most relevant to your question is the
condition they refer to as acquired sociopathy. After small lesions of
the frontal cortex, patients suffer no cognitive deficits, but are
oblivious to the social consequnces of their actions, leading often to
very inappropriate behavior. It seems to stem from an inability to
respond viscerally to socially significant stimuli. Check out the
following references:
Damasio H. Grabowski T. Frank R. Galaburda AM. Damasio AR.
The return of Phineas Gage: clues about the brain from the skull of a
famous patient
Science. 264(5162):1102-5, 1994 May 20.
When the landmark patient Phineas Gage died in 1861, no autopsy was
performed, but his skull was later recovered. The brain lesion that
caused the profound personality changes for which his case became
famous has been presumed to have involved the left frontal region, but
questions have been raised about the involvement of other regions and
about the exact placement of the lesion within the vast frontal
territory. Measurements from Gage's skull and modern neuroimaging
techniques were used to reconstitute the accident and determine the
probable location of the lesion. The damage involved both left and
right prefrontal cortices in a pattern that, as confirmed by Gage's
modern counterparts, causes a defect in rational decision making and
the processing of emotion.
Bechara A. Damasio AR. Damasio H. Anderson SW.
Insensitivity to future consequences following damage to human
prefrontal cortex. Source Cognition. 50(1-3):7-15, 1994
Following damage to the ventromedial prefrontal cortex, humans develop
a defect in real-life decision-making, which contrasts with otherwise
normal intellectual functions. Currently, there is no
neuropsychological probe to detect in the laboratory, and the cognitive
and neural mechanisms responsible for this defect have resisted
explanation. Here, using a novel task which simulates real-life
decision-making in the way it factors uncertainty of premises and
outcomes, as well as reward and punishment, we find that prefrontal
patients, unlike controls, are oblivious to the future consequences of
their actions, and seem to be guided by immediate prospects only. This
finding offers, for the first time, the possibility of detecting these
patients' elusive impairment in the laboratory, measuring it, and
investigating its possible causes.
Saver JL. Damasio AR. Title Preserved access and processing of social
knowledge in a patient with acquired sociopathy due to ventromedial
frontal damage.
Neuropsychologia. 29(12):1241-9, 1991.
Acquired damage to ventromedial frontal cortices produces abnormalities
of decision-making that are especially marked in the realm of social
conduct. The pathogenesis of this disorder remains unexplained. One
possible mechanism posits that patients with lesions of ventromedial
frontal cortices, while retaining the ability to recognize the entities
and events that compose social situations, lose the ability to generate
an appropriate array of response options to social stimuli, and to
conceptualize the future consequences of choosing a particular option.
To explore the validity of this mechanism, we tested a prototypical
patient with bilateral ventromedial frontal injury and social conduct
disorder, along with a group of matched controls, in a series of
laboratory probes designed to examine the manipulation of response
options and projected outcomes to social stimuli. The experimental
subject (patient E.V.R.) exhibited normal or superior performance on
tasks that measure the ability to (1) generate possible response
options to social situations, (2) consider the future consequences of
pursuing particular response options, (3) conceptualize effective
measures to achieve given social objectives, (4) predict the likely
outcome of a particular configuration of social stimuli, and (5)
perform moral reasoning at an advanced developmental level. These
findings suggest that: (1) the base of social knowledge that E.V.R.
acquired during his normal development is still intact; and that (2)
his capacity to access and process components of such knowledge is also
intact, in the conditions specified in our experiment.
Tranel D. Damasio H.
Neuroanatomical correlates of electrodermal skin conductance responses.
Source Psychophysiology. 31(5):427-38, 1994 Sep.
We studied the electrodermal skin conductance responses (SCRs) of 36
subjects with well-characterized lesions in various regions of the
cerebral hemispheres. Several lesion loci were consistently associated
with defective electrodermal responding: the ventromedial frontal
region (right and left), the right inferior parietal region, and the
anterior cingulate gyrus (right and left). Our findings provide direct
information regarding neural correlates of skin conductance responses
in humans.
