frontal lobe anatomy and functions

1. Dr arvind b kulkarni
Resident , DNB neurology
Kasturba medical college , mangalore.

3. Anatomy.
 Frontal lobe extends from the frontal pole to the central sulcus above the
sylvian fissure.
 Central sulcus separates the frontal lobe from parietal lobe . The precentral
sulcus devides the rest of the frontal of lobe from motor strip .
 Comprises upto anterior one-half of each cerebral hemisphere.
 Made up of 4 gyri-
 Precental gyrus [primary motor area]
 sup. Frontal
 middle frontal
 inf. Frontal gyrus.
 SMA- portion of sup frontal gyrus that lies on the medial surface .
 Premotor area lies on the lateral surface .

6. Broadmann’s areas

7. Medial aspect

9. Primary motor cortex
 Frontal agranular cortex [ areas 4 ] – pyramidal cells of
layer v of pre and postcentral convolutions .
( homunculus )
 Contains betz cells – corticospinal and corticobulbar fibers.
 Frontopontocerebellar tract
 Also consists of several parallel fiber systems that pass from
the frontal cortex to the caudate, putamen ,subthalamic,
red nucleus and brainstem reticular formation.
 Lateral area 6- pre motor cortex
 Medial area 6- supplemental motor cortex
 Area 8 - frontal eye fields
 Area 8a – supplementary eye fields .

11. Connections of motor cortex
 Projects to spinal motor neuron to control limb, hand
, foot and digit movements and to appropriate cranial
nerves motor neuron to control facial movements .
 Also projects to basal ganglia and red nucleus.

13. Functions of the premotor cortex
 Premotor region functions primarily to choose
behavior in response to external cues
 Supplementary motor region makes a greater internal
contribution when no such cues are available
.[passingham]
 Supplementary motor area(parts of area 6 that lies on
the medial surface of cerebral hemesphere ) –
selection and direction of motor sequences. (laplan)

14.  Premotor region influences movement directly through
corticospinal projections or indirectly through projections
to the motor cortex .
 Receives projections from the posterior parietal area PE
and PF .
 concerned with execution of limb movements .
 FEF ( area 8 and 8a ) receive projections from regions
controlling eye movements(to the contralateral side ) and
send projections to these regions . Receives input from
posterio parietal region PG and superior colliculus .
 Inferior frontal gyrus- motor speech area ( broca’s area ).

15.  Motor cortex makes the movement
 Premotor cortex selects the movement ( pre motor cortex
neurons discharge even before initiation of actual
movement)
 Prefrontal cortex controls congnitive processes so that
appropriate movements are selected at correct time and
place .
 Internal cues – temporary memory , working memory or
short term memory .
 External cues – behavior controlled by environmental clues
.
 Context cues- behavior varies with the environment .

16. Frontal eye fields
 Saccades or fast eye movements –
 Internally targeted saccades , voluntary ( intentional)-
target searching , memory guided, predictive ( where
appearance of target is anticipated )
 Externally targeted saccades- reflexively activated by
appearance of new target or a sound.
 Spontaneous saccades- occur in the absence of a target
, triggerred internally by both FEF and SC , to
repetitively scan the environment , occur at rest ,
during motor activities , REM sleep .
 Quick phases of nystagmus.

17. Contd.
 FEF  SC three paths
 1. direct pathway – post aspect of ant limb of IC
 Indirect pathway to thalamus ,
 Via CN  SNr  SC in turn tonically supress saccades
by GABA-ergic mechanisms . This controlled
disinhibition is essential for normal visual and
auditory guided sacccades to rememberd saccades.
 DLPFC SC ( via ant limb of IC ) – to supress
unwanted saccades to distracting stimuli when
attention is targeted to an exisiting target .

18.  PEF- no direct involvement in generating saccades
 Connects to FEF and SC – location of potential targets
for orienting .

19. Prefrontal cortex - organ of
civilisation ( halstead,luria )
Anterior to area 6,area 8, and the motor speech
centers are areas referred to as the prefrontal cortex.
it includes areas 9-12 , 32, 45,47 and others .
main projection site for dorsomedial nucleus of
thalamus
Involved in initiation planned action ,executive
control of all mental operations.

20. Prefrontal
cortex
Dorsolateral
prefrontal
cortex DLPFC
Medial
prefrontal
cortex MPC
Orbitofrontal
cortex OFC

21. DLPFC [ areas 9 and 46 ]
 Organisation of self-ordered tasks.
 Working memory .
 Frontal lobe executive function is mainly carried out in
DLPFC.
 Ability to plan, carry out and monitor series of actions
needed to accomplish a goal .
 Oculomotor control- decision making regarding
voluntary eye movements and inhibiting unwanted
reflex saccades.

22.  Recieves its main input from posterior parietal area
and superior temporal sulcus. These connections are
reciprocal .
 Has extensive connections to regions where posterior
parietal cortex also projects ( cingulate cortex , basal
ganglia and superior colliculus )

26. MPC ( area 25 and 32 )
 Has connections with several thalamic nuclei
[dorsomedian ] superior temporal cortex .
 Important in visual and auditory associations.

27. OFC/ inf. Prefrontal cortex
[ area 11-14]
 Important connections with the limbic system
particularly amygdala.
 Recieves main afferents from the temporal lobe
including auditory regions of the superior temporal
gyrus , visual regions of the TE an the superior
temporal sulcus and the amygdala.
 Also there are connections from the somatosensory
cortex area 43 , gustatory cortex [ in the insula ] and
olfactory regions of the pyriform cortex .

43.  Thank you .