Penfield`s Homunculus nowadays: Historical review, anatomy of the



Penfield`s Homunculus nowadays: Historical review, anatomy of the
Penfield's Homunculus nowadays: Historical review,
anatomy of the sensorimotor cortex and cases for clinicalradiological correlation
Poster No.:
ECR 2016
Educational Exhibit
L. Anton Mendez, M. Udondo Gonzalez del Tanago, S. Delgado
Saiz, J. J. gomez muga, M. sarmiento, M. Schuller; Bilbao/ES
Neoplasia, Ischemia / Infarction, Edema, Diagnostic procedure,
MR-Diffusion/Perfusion, MR, CT, Neuroradiology brain, CNS,
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Learning objectives
Anatomy of the somatosensorial and motor cortex in the human brain
To identify the Rolandic fissure in CT/MR neuroimaging
An approach to the history of human sensorimotor cortex topography since
the first researches in animals
To describe the Penfield's homunculus model and its "little" variations
through the time
To provide a number of cases of our institution where an accurate clinicalradiological correlation is demonstrated
The interest for localisation of functions in the brain began in the first quarter if XIX
Probably the first to suggest there was some kind of structural organisation within the
brain functions was Franz Joseph Gall in 1796, with his theory of Phrenology. He believed
the men's intelectual faculties were innat and their manifestation depended on their
organisation in the brain. He proposed that the brain was made of "organs", having each
one the control on a mental faculty. Despite this theory had no scientifical base, it served
as a beginning for lots of investigations that took place in the next century.
Pierre Flourens made pioneering experiments in animals around 1825. They consisted
in surgical ablation and electric stimulation of focal areas of the brain. He also observed
brain lesions in dead patients with neurological symptoms and could demonstrate
convincingly the brain had many divisions responsible for different functions.
Broca and Wernicke continued with this investigations mainly in dead patients with
language disorders and described the small areas in the temporal lobe where the injury
took place in each case.
The first studies with electrostimulation in humans were made by Fedor Krause in 1902.
Between 1930 and 1950 Wilder Penfield, through advanced studies with
electrostimulation in epileptic patients, described a detailed somatotopic map. It was
represented in the book, published in 1950 in co-authority with Theodore Rasmussen
"The cerebral cortex of man: A clinical study of localization and function"
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Findings and procedure details
As Penfield described, the primary motor cortex is located in the frontal lobe, in the named
precentral gyrus, while the primary somatosensory cortex is placed in the postcentral
gyrus in the anterior parietal lobe. Both are separated by the central (or Rolandic) sulcus
and surrounded anteriorly by the precentral sulcus and posteriorly by the postcentral
There are some landmarks than can help us to find the central sulcus in a neuroimaging
(MR/CT) study (Fig. 1):
In an axial view central sulcus can be recognised because of its omega
shape. This is a very constant finding.
The frontal superior sulcus intersects the precentral sulcus, which defines
(anteriorly) the precentral gyrus.
Pars bracket sign: the marginal sulcus is located medial and immediately
posterior to the central sulcus.
In a sagittal view we can find the central sulcus intersecting the posterior
end of the cingular sulcus.
Usually the postcentral gyrus is thinner than the precentral one. We will find
the central sulcus between them.
Somatotopic distribution in both gyri is represented by a topographic map using a coronal
view of each structure, with each part of the body drawn over the cortical level where it
is localised. (Fig. 2 and Fig. 3)
Usually a neuroimaging study made because of focal neurological symptoms shows
pathology in the basal ganglia or white matter, but sometimes an injury in the primary
cortex (following this somatotopic map) can be demonstrated. We must look for it so we
don't miss it when it is present.
We provide four cases of our institution where the symptoms of the patient directly
correlate with an injury in the primary sensorimotor cortex (Figs. 4-8)
Images for this section:
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Fig. 1: Central sulcus in an MRI. Sagittal and axial T1 weighted images. Upper: Central
sulcus intersects the posterior end of the cingular sulcus. Lower: Left: Pars bracket sign.
Marginal sulcus is drawn in green. Also note the omega shape of the central sulcus (red).
Right: Intersection between frontal superior sulcus and precentral sulcus.
© Osakidetza, H. U. Basurto - Bilbao/ES
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Fig. 2: Topographic map of primary motor cortex, located in the precentral gyrus (coronal
© Albert Kok at nl.wikipedia [Public domain]
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Fig. 3: Primary somatosensory cortex topography in postcentral gyrus
© OpenStax College [CC BY 3.0 (]
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Fig. 4: CASE 1: 82 y/o male. 10 hour-long distal left upper limb palsy. Non-enhanced
emergency brain CT. A focal ischaemic area can be appreciated in the right precentral
gyrus. In the coronal reconstruction a correlation between findings and the cortical motor
somatotopic map is demonstrated.
© Osakidetza, H. U. Basurto - Bilbao/ES
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Fig. 5: CASE 2: 65 y/o female. Right lower limb myoclonias of recent onset. Emergency
non-enhanced CT (upper images) and enhanced CT (lower images): Centimetric nodular
enhancing lesion in the left precentral gyrus with perilesional oedema. Patient is referred
to MRI (next image).
© Osakidetza, H. U. Basurto - Bilbao/ES
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Fig. 6: CASE 2 (continuation): axial FLAIR, axial and coronal enhanced T1 and diffusion
sequences of a brain MR which confirms the findings at CT. A central diffusion restriction
can be noted. The coronal reconstruction shows a strong correlation with the motor cortex
somatotopic map. Surgical biopsy: Glioblastoma.
© Osakidetza, H. U. Basurto - Bilbao/ES
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Fig. 7: CASE 3: 43 y/o female. 1 day since the onset of 4/5 left upper limb paresis.
Emergency CT without findings. Axial and coronal diffusion weighted sequences of a
brain MR are shown, where a small acute ischaemic area is present in the precentral
gyrus. A clinical-radiological correlation is demonstrated once again if we compare the
coronal view with the cortical somatotopic map.
© Osakidetza, H. U. Basurto - Bilbao/ES
Page 10 of 12
Fig. 8: CASE 4: 76 y/o female who was admitted to the Neurology department because of
left lower limb 4/5 proximal paresis. Emergency CT was normal. MRI was practised two
days after admission. Diffusion weighted images are shown. A focal diffusion restriction
area is present in the medial precentral gyrus, clinically and radiologically consistent with
a ischaemic acute-subacute lesion.
© Osakidetza, H. U. Basurto - Bilbao/ES
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The advances in neuroscience have allowed us to create a topographic map
of the brain
It is important to localise de Rolandic fissure so we can easily identify the
primary sensorimotor cortex around it
Sometimes we can find a correlation between neurological examination and
radiological findings if we look for it
Having the clinical findings in mind can allow us to make a more accurate
Personal information
1. Naidich TP, Blum JT, Firestone MI. The parasagittal line: an anatomic landmark for
axial imaging. AJNR Am J Neuroradiol. 2001;22 (5): 885-95.
2. Sabatini R. Phrenology: The history of brain localization.
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