Subdivisions of the Frontal Cortex
Frontal lobe = all tissue anterior to the central sulcus = 20% of the neocortex
3 general areas:
Prefrontal cortex = 3 general regions
Dorsolateral prefrontal cortex
Inferior (ventral) prefrontal cortex
o Sometimes called the orbitofrontal
cortex due to relation to eye socket
Medial frontal cortex
Many areas in frontal cortex are multimodal – deal with many different kinds of sensory
A Theory of Frontal Lobe Function
People with frontal-lobe injury cannot handle a situation with many different details. The
main areas of difficulty are:
Planning in advance and selecting from many options
Ignoring extraneous stimuli and focusing on the task at hand
Keep track of past occurrences and chains of events
The frontal lobe contains systems that are implement different behavioural strategies for
dealing with external and internal cues.
Functions of the Premotor Cortex
Motor cortex is the mechanisms for executing individual movements. The premotor
cortex selects the motions to be executed.
This is mainly in response to external cues
The supplementary premotor regions contributes internal cues when there are no
external cues available
The supplementary motor region is involved in the selection and direction of motor
sequences. These are self-paced/internally driven.
Motor acts are driven by cues but can also be associated with cues:
Red means stop. Eye movement:
Can be made towards specific targets or made on basis of internal cues
o Looking at specific objects or just looking around randomly
Functions of the Prefrontal Cortex
Prefrontal cortex handles cognitive processes so that correct movements are chosen at
the right time/place Premotor cortex selects movements Motor cortex is
responsible for executing movements.
Internalized information contains a set of ‘rules’ that guides thoughts and actions.
Temporal memory: neural record of recent events and their order. Can be related to:
Things Object-recognition stream of processing
Movements Motor stream of processing
o Both of these streams project to the frontal cortex (in different places)
which means that there is temporal memory of both streams somewhere
in the cortex
People whose temporal memory is defective depend on external cues on how to act.
Behaviour is controlled completely by external cues.
People with frontal-lobe injuries have a problem inhibiting their actions towards
One type of external cue: feedback about the rewarding properties of stimuli
See a picture of mother. Know mother will give you love and affection. Picture of
mother = feelings of love and affection
The orbitofrontal cortex is essential to learning by association
Behaviour is context-driven behaviour that is appropriate in one situation may very
quickly become inappropriate if some of the context changes even slightly
Frontal lobe is very large in social primates
Choice of behaviour is dependent on sensory information:
Comes from temporal lobe to inferior frontal cortex
It can also depend on affective context – comes from the amygdala
Orbitofrontal injuries (lesions, traumatic brain injury) have difficulty with context,
especially in social situations. Autonoetic Awareness
Def.: autobiographical knowledge that allows us to decide on behaviour after
experiences throughout life.
Allows a person to bind themselves as a continuous entity through time
Impairment in autonoetic awareness leads to a deficit in self-regulation.
Medial and ventral frontal injury patients show this
Asymmetry of Frontal Lobe Function
Left frontal lobe: preferential role in language related movements (speech)
Right frontal lobe: greater role in nonverbal movements (facial expression)
This asymmetry is relative not absolute – people with damage in one lobe don’t
lose all functions related to that lobe. They retain some, which shows that the
other lobe still holds some of the processes.
Bifrontal lesions cannot be duplicated in lesions to either singular hemispheres.
Patients with bifrontal lesions may have problems with proverbs and telling the
time of day, for example
Heterogeneity of Frontal Lobe Functions
Correlations among tasks specific to frontal lobe are very low. Why?
Tasks often require different processes, all linked to different areas of the frontal
Patients will all have different lesions in different areas, meaning that
performance will be affected to different degrees, depending on the location of
Symptoms of Frontal Lobe Regions
Disturbances of Motor Function
Fine Movement, Speed, and Strength
Damage to primary motor cortex chronic loss of ability to make fine, independent
Maybe due to loss of direct corticospinal projections onto motor neurons
Can also lead to loss of speed and strength in limb and hand movements
This can also occur in damage to the prefrontal cortex
Movement Programming Damage to the supplementary motor cortex disruption to all voluntary movements but
this is usually quickly recovered. Only lasting symptom is damage to the performance of
rapidly alternating movements in the fingers or hands
Large lesions in the supplementary motor cortex may only lead to relatively minor
This is due to the fact that both the left and right premotor cortices participate in
Patients with frontal-lobe injuries make more errors in sequence
Components are recalled correctly but in the wrong order
Can also lead to issues in copying facial movements = frontal lobe may have role in
controlling the face
Damage to frontal lobe issues with voluntary gaze
Study: recording patients’ eye movements while looking at complex image
Control – when asked about people’s clothing, would look at a person’s body in
an image. When asked about age, would look at the person’s face.
Person with frontal-lobe damage – when asked same questions, would just look
around image randomly. Change is question about the image didn’t change the
pattern of eye gaze.
Part 1: ability of patients to make voluntary eye motions towards or away from a briefly
appearing target to the left or right of a fixation point.
Normally, a person would make a quick eye movement (saccade) towards a
Person with damage: no issues with this part
Part 2: Patients had to move eyes to same spot as the target had appeared on an
opposite visual field. This meant – limiting normal voluntary saccade and making a
voluntary saccade in opposite direction
Patients with damage had two issues with this:
o Couldn’t limit normal voluntary saccade
o Couldn’t make eye movements in contralateral direction to the damaged
Pushing on eyeball = world moves. Move eyes = world stays stable. Corollary discharge (reafference): a neural signal is needed to make the eyes move and
other is needed to warn that the movement is going to happen.
Moves eyes mechanically: there is no signal and world moves
Moves eyes normally: signals and the world stays still
Voluntary eye movements need two sets of signals:
1. Movement command (through the motor system) effects the movement
2. Signal (corollary discharge) goes from frontal lobe to parietal and temporal
association cortex prepares the sensory system for the movement
This means that a person’s sensory system can interpret changes in the world due to
information about movement.
Frontal lobe lesion can disturb movement of voluntary eye gaze and the signal to the
rest of the brain that a movement is about to take place
Evidence of frontal lobe participation in corollary discharge:
Some cells in frontal eye fields fire simultaneously with eye movement
They seem to monitor ongoing movement, a process very similar to corollary
Frontal lobe has two speech zones:
Broca’s area – selects words on basis of cues
Supplementary speech area – required to find words with no external cues
Damage to Broca’s area agrammatism: impairment in ability to use verbs and
produce appropriate grammar
Damage to supplementary area (occurs with strokes) may result in becoming mute
Unilateral damage: ability to speak may come back after a few weeks
Bilateral damage: ability will not come back
Loss of Divergent Thinking
Posterior region lesions = decrease in IQ scores. Frontal lobe lesions do not but
mistakes are still made.
Theory that IQ tests measure convergent thinking: the idea that there is only one
answer to every question.
Examples: definitions, puzzles, etc.
Other tests measure divergent thinking: where number and variety of answers to a
single question is emphasized. Lesions to the frontal lobe interfere with this kind of thinking
Frontal-lobe damage general loss of spontaneity
Thurstone Word Fluency test: write as many words as possible starting with this letter in
5 minutes. Write as many four-letter words as possible starting with another letter in 4
People with lesions often have a very low output in this test
This seems to occur when there is damage to the left orbitofrontal region. However,
lesions to the right orbitofrontal region may result in loss of verbal fluency
Test with Mrs. P – damage to right frontal lobe. 4 features of frontal lobe damage when
she was given the test:
1. Low output of words
2. Rule breaking – didn’t write four-letter words on second part of test. She
understood the instructions but couldn’t organize her behaviour to follow them
3. Writing was very jerky
4. Kept talking and looking around the room during the test – diminished attention
= loss of verbal spontaneity
Study: verbal-fluency deficit