Historical origins
1848 edition of American Phrenological Journal published by Fowlers & Wells, New York City
Phrenology, created by Franz Joseph Gall
(1758–1828) and Johann Gaspar Spurzheim (1776–1832) and best known for
the idea that one's personality could be determined by the variation of
bumps on their skull, proposed that different regions in one's brain
have different functions and may very well be associated with different
behaviours.
Gall and Spurzheim were the first to observe the crossing of pyramidal
tracts, thus explaining why lesions in one hemisphere are manifested in
the opposite side of the body. However, Gall and Spurzheim did not
attempt to justify phrenology on anatomical grounds. It has been argued
that phrenology was fundamentally a science of race. Gall considered the
most compelling argument in favor of phrenology the differences in
skull shape found in sub-Saharan Africans and the anecdotal evidence
(due to scientific travelers and colonists) of their intellectual
inferiority and emotional volatility. In Italy, Luigi Rolando carried out lesion experiments and performed electrical stimulation of the brain, including the Rolandic area.
Phineas Gage's accident
Phineas Gage became one of the first lesion case studies in 1848 when an explosion drove a large iron rod completely through his head, destroying his left frontal lobe.
He recovered with no apparent sensory, motor, or gross cognitive
deficits, but with behaviour so altered that friends described him as
"no longer being Gage," suggesting that the damaged areas are involved
in "higher functions" such as personality. However, Gage's mental changes are usually grossly exaggerated in modern presentations.
Subsequent cases (such as Broca's patient Tan) gave further support to the doctrine of specialization.
Major theories of the brain
Currently,
there are two major theories of the brain's cognitive function. The
first is the theory of modularity. Stemming from phrenology, this theory
supports functional specialization, suggesting the brain has different
modules that are domain specific in function. The second theory,
distributive processing, proposes that the brain is more interactive and
its regions are functionally interconnected rather than specialized.
Each orientation plays a role within certain aims and tend to
complement each other (see below section `Collaboration´).
Modularity
The
theory of modularity suggests that there are functionally specialized
regions in the brain that are domain specific for different cognitive
processes. Jerry Fodor
expanded the initial notion of phrenology by creating his Modularity of
the Mind theory. The Modularity of the Mind theory indicates that
distinct neurological regions called modules
are defined by their functional roles in cognition. He also rooted many
of his concepts on modularity back to philosophers like Descartes, who
wrote about the mind being composed of "organs" or "psychological
faculties". An example of Fodor's concept of modules is seen in
cognitive processes such as vision, which have many separate mechanisms
for colour, shape and spatial perception.
One of the fundamental beliefs of domain specificity and the theory of modularity suggests that it is a consequence of natural selection
and is a feature of our cognitive architecture. Researchers Hirschfeld
and Gelman propose that because the human mind has evolved by natural
selection, it implies that enhanced functionality would develop if it
produced an increase in "fit" behaviour. Research on this evolutionary
perspective suggests that domain specificity is involved in the
development of cognition because it allows one to pinpoint adaptive
problems.
An issue for the modular theory of cognitive neuroscience is that
there are cortical anatomical differences from person to person.
Although many studies of modularity are undertaken from very specific
lesion case studies, the idea is to create a neurological function map
that applies to people in general. To extrapolate from lesion studies
and other case studies this requires adherence to the universality assumption,
that there is no difference, in a qualitative sense, between subjects
who are intact neurologically. For example, two subjects would
fundamentally be the same neurologically before their lesions, and after
have distinctly different cognitive deficits. Subject 1 with a lesion
in the "A" region of the brain may show impaired functioning in
cognitive ability "X" but not "Y", while subject 2 with a lesion in area
"B" demonstrates reduced "Y" ability but "X" is unaffected; results
like these allow inferences to be made about brain specialization and
localization, also known as using a double dissociation.
The difficulty with this theory is that in typical non-lesioned
subjects, locations within the brain anatomy are similar but not
completely identical. There is a strong defense for this inherent
deficit in our ability to generalize when using functional localizing
techniques (fMRI, PET etc.). To account for this problem, the
coordinate-based Talairach and Tournoux stereotaxic system
is widely used to compare subjects' results to a standard brain using
an algorithm. Another solution using coordinates involves comparing
brains using sulcal reference points. A slightly newer technique is to use functional landmarks,
which combines sulcal and gyral landmarks (the groves and folds of the
cortex) and then finding an area well known for its modularity such as
the fusiform face area. This landmark area then serves to orient the researcher to the neighboring cortex.
Future developments for modular theories of neuropsychology may
lie in "modular psychiatry". The concept is that a modular understanding
of the brain and advanced neuro-imaging techniques will allow for a
more empirical diagnosis of mental and emotional disorders. There has
been some work done towards this extension of the modularity theory with
regards to the physical neurological differences in subjects with
depression and schizophrenia, for example. Zielasek and Gaeble have set
out a list of requirements in the field of neuropsychology in order to
move towards neuropsychiatry:
- To assemble a complete overview of putative modules of the human mind
- To establish module-specific diagnostic tests (specificity, sensitivity, reliability)
- To assess how far individual modules, sets of modules or their connections are affected in certain psychopathological situations
- To probe novel module-specific therapies like the facial affect recognition training or to retrain access to context information in the case of delusions and hallucinations, in which "hyper-modularity" may play a role [8]
Research in the study of brain function can also be applied to cognitive behaviour therapy.
As therapy becomes increasingly refined, it is important to
differentiate cognitive processes in order to discover their relevance
towards different patient treatments. An example comes specifically from
studies on lateral specialization between the left and right cerebral
hemispheres of the brain. The functional specialization of these
hemispheres are offering insight on different forms of cognitive
behaviour therapy methods, one focusing on verbal cognition (the main
function of the left hemisphere) and the other emphasizing imagery or
spatial cognition (the main function of the right hemisphere). Examples of therapies that involve imagery, requiring right hemisphere activity in the brain, include systematic desensitization and anxiety management training.
Both of these therapy techniques rely on the patient's ability to use
visual imagery to cope with or replace patients symptoms, such as
anxiety. Examples of cognitive behaviour therapies that involve verbal
cognition, requiring left hemisphere activity in the brain, include
self-instructional training and stress inoculation.
Both of these therapy techniques focus on patients' internal
self-statements, requiring them to use vocal cognition. When deciding
which cognitive therapy to employ, it is important to consider the
primary cognitive style of the patient. Many individuals have a tendency
to prefer visual imagery over verbalization and vice versa. One way of
figuring out which hemisphere a patient favours is by observing their
lateral eye movements. Studies suggest that eye gaze reflects the
activation of cerebral hemisphere contralateral to the direction. Thus,
when asking questions that require spatial thinking, individuals tend to
move their eyes to the left, whereas when asked questions that require
verbal thinking, individuals usually move their eyes to the right.
In conclusion, this information allows one to choose the optimal
cognitive behaviour therapeutic technique, thereby enhancing the
treatment of many patients.
Areas representing modularity in the brain
Fusiform face area
One of the most well known examples of functional specialization is the fusiform face area (FFA). Justine Sergent
was one of the first researchers that brought forth evidence towards
the functional neuroanatomy of face processing. Using positron emission
tomography (PET), Sergent found that there were different patterns of
activation in response to the two different required tasks, face
processing verses object processing.
These results can be linked with her studies of brain-damaged patients
with lesions in the occipital and temporal lobes. Patients revealed that
there was an impairment of face processing but no difficulty
recognizing everyday objects, a disorder also known as prosopagnosia. Later research by Nancy Kanwisher using functional magnetic resonance imaging (fMRI), found specifically that the region of the inferior temporal cortex, known as the fusiform gyrus,
was significantly more active when subjects viewed, recognized and
categorized faces in comparison to other regions of the brain. Lesion
studies also supported this finding where patients were able to
recognize objects but unable to recognize faces. This provided evidence
towards domain specificity in the visual system, as Kanwisher acknowledges the Fusiform Face Area as a module in the brain, specifically the extrastriate cortex, that is specialized for face perception.
Visual area V4 and V5
While looking at the regional cerebral blood flow (rCBF), using PET, researcher Semir Zeki directly demonstrated functional specialization within the visual cortex known as visual modularity. He localized regions involved specifically in the perception of colour and vision motion. For colour, visual area V4 was located when subjects were shown two identical displays, one being multicoloured and the other shades of grey. This was further supported from lesion studies where individuals were unable to see colours after damage, a disorder known as achromatopsia. Combining PET and magnetic resonance imaging
(MRI), subjects viewing a moving checker board pattern verses a
stationary checker board pattern located visual area V5, which is now
considered to be specialized for vision motion. (Watson et al., 1993)
This area of functional specialization was also supported by lesion
study patients who's damage caused cerebral motion blindness.
Frontal lobes
Studies have found the frontal lobes to be involved in the executive functions of the brain, which are higher level cognitive processes.
This control process is involved in the coordination, planning and
organizing of actions towards an individual's goals. It contributes to
such things as one's behaviour, language and reasoning. More
specifically, it was found to be the function of the prefrontal cortex,
and evidence suggest that these executive functions control processes
such as planning and decision making, error correction and assisting
overcoming habitual responses. Miller and Cummings used PET and
functional magnetic imaging (fMRI) to further support functional
specialization of the frontal cortex. They found lateralization of
verbal working memory in the left frontal cortex and visuospatial
working memory in the right frontal cortex. Lesion studies support these
findings where left frontal lobe patients exhibited problems in
controlling executive functions such as creating strategies. The dorsolateral, ventrolateral and anterior cingulate
regions within the prefrontal cortex are proposed to work together in
different cognitive tasks, which is related to interaction theories.
However, there has also been evidence suggesting strong individual
specializations within this network.
For instance, Miller and Cummings found that the dorsolateral
prefrontal cortex is specifically involved in the manipulation and
monitoring of sensorimotor information within working memory.
Right and left hemispheres
During the 1960s, Roger Sperry
conducted a natural experiment on epileptic patients who had previously
had their corpora callosa cut. The corpus callosum is the area of the
brain dedicated to linking both the right and left hemisphere together.
Sperry et al.'s experiment was based on flashing images in the right and
left visual fields of his participants. Because the participant's
corpus callosum was cut, the information processed by each visual field
could not be transmitted to the other hemisphere. In one experiment,
Sperry flashed images in the right visual field (RVF), which would
subsequently be transmitted to the left hemisphere (LH) of the brain.
When asked to repeat what they had previously seen, participants were
fully capable of remembering the image flashed. However, when the
participants were then asked to draw what they had seen, they were
unable to. When Sperry et al. flashed images in the left visual field
(LVF), the information processed would be sent to the right hemisphere
(RH) of the brain. When asked to repeat what they had previously seen,
participants were unable to recall the image flashed, but were very
successful in drawing the image. Therefore, Sperry concluded that the
left hemisphere of the brain was dedicated to language as the
participants could clearly speak the image flashed. On the other hand,
Sperry concluded that the right hemisphere of the brain was involved in
more creative activities such as drawing.
Parahippocampal place area
Located in the parahippocampal gyrus,
the parahippocampal place area (PPA) was coined by Nancy Kanwisher and
Russell Epstein after an fMRI study showed that the PPA responds
optimally to scenes presented containing a spatial layout, minimally to
single objects and not at all to faces.
It was also noted in this experiment that activity remains the same in
the PPA when viewing a scene with an empty room or a room filled with
meaningful objects. Kanwisher and Epstein proposed "that the PPA
represents places by encoding the geometry of the local environment".
In addition, Soojin Park and Marvin Chun posited that activation in the
PPA is viewpoint specific, and so responds to changes in the angle of
the scene. In contrast, another special mapping area, the retrosplenial cortex (RSC), is viewpoint invariant or does not change response levels when views change. This perhaps indicates a complementary arrangement of functionally and anatomically separate visual processing brain areas.
Extrastriate body area
Located
in the lateral occipitotemporal cortex, fMRI studies have shown the
extrastriate body area (EBA) to have selective responding when subjects
see human bodies or body parts, implying that it has functional
specialization. The EBA does not optimally respond to objects or parts
of objects but to human bodies and body parts, a hand for example. In
fMRI experiments conducted by Downing et al. participants were asked to
look at a series of pictures. These stimuli includes objects, parts of
objects (for example just the head of a hammer), figures of the human
body in all sorts of positions and types of detail (including line
drawings or stick men), and body parts (hands or feet) without any body
attached. There was significantly more blood flow (and thus activation)
to human bodies, no matter how detailed, and body parts than to objects
or object parts.
Distributive processing
The
cognitive theory of distributed processing suggests that brain areas
are highly interconnected and process information in a distributed
manner.
A remarkable precedent of this orientation is the research of Justo Gonzalo on brain dynamics
where several phenomena that he observed could not be explained by the
traditional theory of localizations. From the gradation he observed
between different syndromes in patients with different cortical lesions,
this author proposed in 1952 a functional gradients model,
which permits an ordering and an interpretation of multiple phenomena
and syndromes. The functional gradients are continuous functions through
the cortex describing a distributed specificity, so that, for a given
sensory system, the specific gradient, of contralateral character, is
maximum in the corresponding projection area and decreases in gradation
towards more "central" zone and beyond so that the final decline
reaches other primary areas.
As a consequence of the crossing and overlapping of the specific
gradients, in the central zone where the overlap is greater, there would
be an action of mutual integration, rather nonspecific (or multisensory) with bilateral character due to the corpus callosum.
This action would be maximum in the central zone and minimal towards
the projection areas. As the author stated (p. 20 of the English
translation)
"a functional continuity with regional variation is then offered, each
point of the cortex acquiring different properties but with certain
unity with the rest of the cortex. It is a dynamic conception of quantitative localizations".
A very similar gradients scheme was proposed by Elkhonon Goldberg in 1989.
Other researchers who provide evidence to support the theory of distributive processing include Anthony McIntosh and William Uttal,
who question and debate localization and modality specialization within
the brain.
McIntosh's research suggests that human cognition involves interactions
between the brain regions responsible for processes sensory information,
such as vision, audition, and other mediating areas like the prefrontal
cortex. McIntosh explains that modularity is mainly observed in sensory
and motor systems, however, beyond these very receptors, modularity
becomes "fuzzier" and you see the cross connections between systems
increase.
He also illustrates that there is an overlapping of functional
characteristics between the sensory and motor systems, where these
regions are close to one another. These different neural interactions
influence each other, where activity changes in one area influence other
connected areas. With this, McIntosh suggest that if you only focus on
activity in one area, you may miss the changes in other integrative
areas. Neural interactions can be measured using analysis of covariance in neuroimaging.
McIntosh used this analysis to convey a clear example of the
interaction theory of distributive processing. In this study, subjects
learned that an auditory stimulus signalled a visual event. McIntosh
found activation (an increase blood flow), in an area of the occipital cortex, a region of the brain involved in visual processing,
when the auditory stimulus was presented alone. Correlations between
the occipital cortex and different areas of the brain such as the prefrontal cortex, premotor cortex and superior temporal cortex showed a pattern of co-variation and functional connectivity.
Uttal focusses on the limits of localizing cognitive processes in
the brain. One of his main arguments is that since the late 90's,
research in cognitive neuroscience has forgotten about conventional psychophysical
studies based on behavioural observation. He believes that current
research focusses on the technological advances of brain imaging
techniques such as MRI and PET scans.
Thus, he further suggest that this research is dependent on the
assumptions of localization and hypothetical cognitive modules that use
such imaging techniques to pursuit these assumptions. Uttal's major
concern incorporates many controversies with the validly,
over-assumptions and strong inferences some of these images are trying
to illustrate. For instance, there is concern over the proper
utilization of control images in an experiment. Most of the cerebrum
is active during cognitive activity, therefore the amount of increased
activity in a region must be greater when compared to a controlled area.
In general, this may produce false or exaggerated findings and may
increase potential tendency to ignore regions of diminished activity
which may be crucial to the particular cognitive process being studied.
Moreover, Uttal believes that localization researchers tend to ignore
the complexity of the nervous system. Many regions in the brain are
physically interconnected in a nonlinear system, hence, Uttal believes
that behaviour is produced by a variety of system organizations.
Collaboration
The
two theories, modularity and distributive processing, can also be
combined. By operating simultaneously, these principles may interact
with each other in a collaborative effort to characterize the
functioning of the brain. Fodor himself, one of the major contributors
to the modularity theory, appears to have this sentiment. He noted that
modularity is a matter of degrees, and that the brain is modular to the
extent that it warrants studying it in regards to its functional
specialization.
Although there are areas in the brain that are more specialized for
cognitive processes than others, the nervous system also integrates and
connects the information produced in these regions. In fact, the
proposed distributive scheme of the functional cortical gradientes by J. Gonzalo
already tries to join both concepts modular and distributive: regional
heterogeneity should be a definitive acquisition (maximum specificity in
the projection paths and primary areas), but the rigid separation
between projection and association areas would be erased through the
continuous functions of gradient.
The collaboration between the two theories not only would provide
a more unified perception and understanding of the world but also make
available the ability to learn from it.
