4 walk along back half

Lecture 4: A Walk Along the Cortex: I.
The Back Half
1. Gordon Holmes and Holes in the Head
2. Wilder Penfield and Brain Stimulation
3. A map of the body-The Somatosensory “Strip”
4. The concept of “receptive field”


An Anthropologist
on Mars
Sacks, Oliver
305.908 Sac

5 in 3-day loan….

not req’d---but just
in case….






Gordon Holmes (18761966)
* British neurologist
(London)
* patients with “penetrating
missile wounds”
* the “visual field” is mapped
in an orderly way in the
contralateral occipital lobe

visual field - the region in which visual targets
can be detected (tested while fixating)


Visual field “defects” (“scotomas”)
hemianopia - patient is unable to see in the
contralateral visual field


Visual field “defects” (“scotomas”)
quadrantanopia - patient is unable to see in the
upper or lower contralateral quadrant


Visual field “defects” (“scotomas”)
scotoma - any visual field defect (can be
smaller than hemi or quadrananopia)



from Docherty et al. (2003). Visual field representations and
locations of visual areas V1/2/3 in human visual cortex.
Journal of Vision, 3, 586-598.


The visual pathway to primary visual cortex
optic nerves - carry information from the

retinal ganglion cells as far as the optic
chiasm


The visual pathway
to primary visual
cortex
optic chiasm - the
place where half of
the information from
each eye crosses
over to the other side
of the brain


The visual pathway to primary visual cortex
optic tracts - the two visual pathways from
chiasm to the visual part of the thalamus


The visual pathway to primary visual cortex
optic radiations – “two” pathways from visual
thalamus to primary visual cortex



Keir et al. (2004). MR imaging of the temporal Stem: anatomic dissection tractography
of the uncinate fasciculus, inferior occipitofrontal fasciculus, and Meyer’s loop of the
optic radiation. American Journal of Neuroradiology, 25, 677–691.

Wilder Penfield (1891-1976)
* Canadian neurosurgeon
* surgical removal of “bad bits”
of cortex for treating
“intractable” epilespsy
* electrical stimulation of
cortex in awake patients



homunculous - “little man” - a
representation of the body surface in a
region of the brain