Prefrontal Lobe Function and Cognitive Processes
by Debra Pizzuto
Group Project-Neuropsychology
Evolution of the pre-frontal lobes in the brain distinguishes humans
from other mammals. Explanation of cognitive function relates to
organization and function of the frontal cortex through a complex
integration of neural networks. Combined with theories from cognitive
psychology, cognitive science, biomedicine, and developmental
psychology, neuropsychologists have developed mechanical testing
devices to further understand functions and structures. Frontal lobes
are the most recent development of the four lobes in the brain. They
comprise one third of the cerebral cortex. Initial planning, strategy
formation, goal setting, maintenance and regulation of behavior,
ability to concentrate, selectively attend and manage shifts in
attention in working memory are functions of the frontal lobes related
to cognition. (Carter,1999). Early stages of cortical processing
develop structural changes in neural fiber tracts. Focus and
attention on visual stimulus, a pre-cognitive condition can be
explained in terms of human development, because neural maturation is
simultaneous with human development and cognitive processing.
Electro-chemical neural potentials are triggered through environmental
interactions that stimulate biological characteristics of excitation or
inhibition of neural connections. Integration of neural information is
sent to associated cortices for further processing, producing cognitive
development from selective attentional information in visual and
sensory stimulus.
The two hemispheres, composed of an outer layer of grey matter
called cortical substance, then white matter, also contain a number of
creases and folds underneath called fissures and sulci. Frontal lobes,
right and left, are separated by the great longitudinal fissure,
separating the two hemispheres. Located at the anterior end of the
frontal cortex base, the prefrontal cortex provides reciprocal neural
connections between more centrally located cortices in combination with
the corpus callosum, the thick band of neural fibers that allows
communication between the two hemispheres. Development of number and
extent of the convolutions appears to have a close relationship to
intellectual power. At birth, convolutions are simpler, sulci are more
shallow, compared to those which have deepened with age and
intellectual function (Gray,645).
Functions of Cerebral cortex include: the ability to analyze sensory
data, perform memory functions, learn new information, form thoughts
and make decisions. The left hemisphere is responsive to systematic,
logical interpretation, production of symbolic information,
mathematics, abstract reasoning, and memory stored in a language
format. Right hemispheric function is holistic. It processes visual
and spacial skill information. Memory is stored in auditory, visual
and spatial modalities (Peterson and Kelly 1998). Geographically
distinct, the frontal, temporal, parietal, and occipital lobes
interconnect with prefrontal lobes associating neural information to
different cortices (Gholson 180). Temporal lobe is responsive to
audition and memory, with preference for left side dominance in speech
production. Parietal areas respond to differences in spatial relations
and somatosensation. Occipital responds to process visual imagery.
The significance of asymmetry is attributable to neural
production with neurons being the primary functional anatomic unit of
the nervous system. Typical neurons are made up of cell body,
dendrites, axon, and a presynaptic terminal. Nucleus containing cell
bodies hold synthesis material for life. Dendrites receive stimuli and
conduct impulses generated by those stimuli to the nerve cell body.
Axon single fibers extend to other parts of the nervous system or to
muscle or glands. They range up to over a meter in length, conducting
away from the cell body. Axon ends have fine branches, each ending is
called a presynaptic terminal. These terminals contact receptive
surfaces of other cells,(postsynaptic cells), transmitting chemical or
electrical information about the neuron to other neurons. The point of
contact is called the synapse. Receptive surfaces including cell body
membrane, dendrites, and synaptic terminals continually process
information signals through the brain while we are recognizing,
planning, and acting on our thoughts. The development of the
prefrontal cortex in humans monitors performance regulating behavior.
Cognitive, developmental and neuropsychological theories agree that
early sensory experiences in life shape later brain behavior
(Paus,1999).
As humans develop, after the first few years of birth,
maturation of neurons involves the development of several fatty
layers of cells called myelin that together form a sheath of
insulation, speeding their impulses. Interneural synapses in the brain
are comprised of action potentials in presynaptic neurons causing a
release of neurotransmitters from synaptic terminals. The transmitter
substance either excites(depolarizes), causing an impulse, or inhibits
(hyperpolarizes) postsynoptic neural membrane resulting in no impulse.
Responses graded as all or none behavior of action potentials transmit
along axons. Event related potential is maintained by the chemically
ionic sodium-potassium pump. Signals stimulate cells, sodium channels
open, more sodium rushes in causing depolarization. The actual signals
operate in grid formations.
Prefrontal cortex is thought to have the function maintaining
cognitive behavior as an essential for planning, setting goals, and
regulating behavior, utilizing the ability to concentrate, attend, and
elaborate thought from associated cortices.
Jean Piagets= early psychological development theories remain
principle proponents for cognitive development. His ideas integrate
biology and epistemology. His concepts of memory, object permanence
and conservation, classification of implicit, working and long term
memory are representative of interactions between humans and the
external world. According to Piaget, developing structures enable
human comprehension and assimilation. His theory of Aschemas@ as
sensorimotor concepts being a system of age relationships dates back to
his work in 1952 (Wolman,4). The importance of selective attention has
been measured as a component of intelligence. His theories also support
lateralization and localized functions of development in the two
hemispheres (Gholson,180). His theory supported examples of perceptual
images recalled from memory, regulated by the prefrontal cortex. We
have since discovered visual long term memory is stored in temporal
cortices, retrieval is signaled back under executive control of the
prefrontal cortex. Frontal areas mediate working memory with two of
the fundamental executive processes being selective attention and task
management (E.Smith and J.Jonides 1999). Research evidences areas for
selective attention with comparison of divided attention and focused
attention (Hale and Lewis,285).
Perceiving sensory experiences is related to attention processes.
Attention fits with our perception when performance is good. Selection
of attention and utility information for performance ideally coincide.
Selective attention is efficient performance with utility for a
specific task. Everything psychological is simultaneously biological,
except neural encoding doesn=t require learning, just experience
(Gazzaniga,74) Study of neural science suggests that psychological
components of attending, planning and acting are developmental elements
of brain function. It seems that function and mechanism complement
each other. Representing cognitive functions have physical brain
structures, mechanisms and internal representations supporting them
(Gazzaniga,135). Explanation of theoretical processing of information
from the environment through the eyes refers to light intensity
measurements that register over the 120 million rods and cone in each
eye. According to theory, the vision system has constructed an
economical way to represent incoming information called edge
representation. Distinctions of boundaries between objects is seen
because of intensity changes in light(Gazzaniga,136). While this is
occurring, mental representation of the object is recorded in
prefrontal working areas for identification and further processing to
associated cortices. Mechanical interactions in the cortex cooperating
as networks of neurons, cross-correlating neural detections generate
network capacities. Changes in connectivity equals neural
conditioning.
Another cognitive theory originated by Badeley, explains frontal
lobe function with the example of >central executive= by which incoming
information according to theory is networked through a phonological
loop, as part of working memory, then assimilated in other cortices.
Strong connectons are stored in long term memory for classification
hierarchically. Reciprocal sensory information is synthesized by
executive control capacity back to prefrontal areas. Cognitive
psychological testing has also determined the left side function as
active processing verbal code, words and vocabulary. Experiments where
patients perform dichotic tasks simultaneously, show right side
prefrontal areas active when attending to nonverbal codes, and visible
features as nameable objects.
Neurophysiological explanations of exactly how the brain monitors
performance regulating behavior remains unanswered. Selective
attention occurs resulting from repeated patterns of identification and
electro-chemical activity competing for dominance. Selective survival
may be through cognitive processes that are products of feature
detection patterns resonating electro-chemically with stored patterns
in the brain.
Diagnostic instruments designed for neuropsychological tests of
brain behavior include: hand held electrical probes that produce low
level stem directly to the brain, positron emission tomography (pet),
functional magnetic resonance imagery (MRI), event related potentials
(ERPs). Averaging scalp potentials through patterns in waveform,
measures brain reaction time and locations. ERP=s can be exacted from
(EEG),electroencephalogram readings(Posner, 333). Micro electrodes
used in animal studies have recently been able to detect visual
attention with ability to see task dependent variables matching
(Posner,335). Differences between right and left thalemic connections
are interesting in that direct stimulus to the left thalamus while
showing complex shapes for identification, will be ignored producing
many errors. Selective attention is directed for retaining information
in that region, displayed by improvement in recall that happens later
(Calvin,86).
Cognitive psychological tools as testing devices for patients
undergoing diagnostic imagery projections help diagnose patients with
traumatic brain injury, lesions, and seizure activity with behaviors
associated with these problems.
According to William H. Calvin, a neurophysiologist at the
University of Washington, precise problems and diagnosis of injury to
the pre-frontal cortex is subtle and under diagnosed. Symptoms are ill
defined and characterized as lack of ability to plan ahead, maintain an
objective or plan, and monitor progress. Problems include
organization of sequence where known variables can=t be organized.
Emotional affect, lacking emotion in responses, due to the decrease in
metabolic activity. When ability to abstract information is lost,
associated cortices responsive to higher cognitive functioning for
concrete thinking needed for comprehension is also fragmented.
Perseveration, behavior that repeated over and over without selective
attention is a much stronger symptom. Severe damage to the frontal
lobe can leave akinetic response, where a person just sits there
Likewise, lesions in cortical regions affect frontal lobe
reciprocation. Operations done to decrease the severity of epileptic
seizures involved cutting parts of the corpus callosum,(split-brain
patients), the structure that function as a bundle of nerve fibers
connecting the two hemispheres shows that left hemisphere is active in
language and verbal information, where right hemisphere is more visual
perception and recognition of emotion. Tests of language, knowledge
retention, and response to cognitive interactions (Gazzangia, 201-205).
Many of these delicate balances within the brain can be seen through
MRI. Operating with hydrogen density of high spatial resolution,
(MRI)=s produce no harmful side affects to patients, healthy brains can
be compared to injured ones. The strong magnetic field measures
changes in magnetic orientation of nuclei in atoms that make up the
tissue of the brain (Posner,326). Currents in neurons give rise to
magnetic and electric fields. MRI=s are more easily localized measures
computed with super conducting magnetometers (Posner and Gazzangia,
328). These results continually indicate there is a delicate balance
between intrinsic neuronal excitation and inhibition for fine tuning
experience-dependent plasticity in the neocortex. MRI measures
attention to environmental stimulus representing an individual ability
to integrate information over time to associative areas of the cortex
by picking up neural activity of the process while testing. Areas of
motor cortex (movement), pre-motor cortex (storage of movement
patterns), parietal lobe, (processing sensory input and sensory
discrimination), occipital lobe (visual interpretation), temporal lobe
(auditory reception), expressed behavior and language in terms of
receptive speech as well as memory information retrieval. Broca=s area,
named after French surgeon, Paul Broca who theorized that damage to the
left lower rear region in front of the motor strip left patients
lacking ability in production of language output is identified
diagnostically with (MRI). Today this type of lesion is termed
>expressive aphasia=(Calvin,43). Wernicke=s area for receptive aphasia,
located near Broca=s, leaves people who have damage in this area unable
to produce speech that makes sense. Many talk excessively, not making
sense. The inference is that language involves transfer of what is
heard or read (Calvin,44). Revealing a multiplicity of
parallel channels and cognitive subsystems specialized for different
elementary cognitive operations, research has found that connectivity
in the brain is rich and generally reciprocal as well as highly
selective. According to (MRI), subsystems are not characterized as
uniquely >central= (Posner,643).
Neuropsychology suggests that selective attention has a relationship
with brain capacity in terms of selection for potential control of
action, coordination, segregation, time constraints and multiple goal
behavior. Characteristic of human intelligence and cognitive concepts
of imagination with distinct considerations for planning provide one
with better focus on various tasks because neural interconnections
strengthen with practice. Conscious attention and focus on a stimulus
act as a catalyst. Flexible relationships explain how the concept
metaphor is comprehended through associations. Metaphor and analogy
permit the use of auxiliary structures that can be used as supplemental
models in reasoning (Posner,820). According to Collins and
Genter(1987),in Attention and Cognitive Development, this process
allows people to create new mental models about what should happen in
various situations in the real world. Sequencing capacity also yields
flexibility for higher order cognitions of naming and reading.
Processing unfamiliar information through neural links with more
familiar fragments of information influences fluid intelligence, the
ability to modify neural circuitry and genetic material. Studies in
creative confusion offer multiple levels of abstraction and sequencing:
rules relating to logic. These are possible explanation to why we keep
re-arranging information finding something better through our
perceptions of concepts and analysis of data.
In conclusion, knowledge gained through experiments offers
logical explanations of organization in the central nervous system.
Study of functions, both normally and abnormally, offers a comparative
analysis further evaluation in the related fields. Modern medicine,
developmental psychologists, cognitive psychologists, and
neuropsychological professions will continue to probe questions of
human processes and function. For now, technology seems to show us the
clearest answers about how we utilize our mind-brain connections.
References
Calvin, William H. (1998). The Cerebral Code, Thinking a thought
in the mosaics of the mind. Cambridge, MA: MIT.
Calvin, W., & Ojemann,G. (1994). Conversations with Neil=s Brain,
The neural nature of thought and language. Reading, MA: Perseus Books.
Carter et.al. (1999). Anterior Cingulate Cortex, Error
Detection, and the Online Monitoring of Performance: An overview
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Greenfield, Susan A. (1997). The Human Brain. New York, NY:
Basic Books.
Gazzaniga, Michael S. (1984). Handbook of Cognitive
Neuroscience. New York, NY: Plenum Press.
Gray, Henry, F.R.S. (1974). Gray=s Anatomy. Philadelphia, PA:
Running Press.
Hale, G., & Lewis, M. (Eds.). (1979). Attention and Cognitive
Development. New York, NY: Plenum Press.
Posner,M.I. (Ed.). (1989). Foundations of Cognitive Science. MA:
MIT Press.
Smith, E., & Jonides, J. (1999). Storage and Executive Processes
in the Frontal Lobes: An overview [Abstract] Science 283,1657-1661.
Retrieved November 15,1999 from the World Wide Web:
http://www.sciencemag.org/cgi/content/ab1.html
Wolman,B., & Stricker,G. (Eds.). (1982). Handbook of Developmental Psychology. Englewood
Cliffs, NJ: Prentice Hall.
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This page last edited 19 - November, 1999
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