Neuroscience Exam # 3
-Sensory Experience and Sensory Reality
• Sound as we perceive it does not exist without a brain to create
it. The only reason that we experience sound is that the
information from the ear goes to a region of the brain that
converts the neural activity into what we then perceive to be
• Synesthesia: the capacity to join sensory experiences across
modalities. A particular sound will also produce a color or taste.
• Winderickx study: provided the first evidence that normal
variation in our mental world is traceable to normal variation in
-Analyzing Sensory Information
• The brain processes visual information in multiple ways. Some
processing allows us to consciously analyze visual stimuli,
whereas other processing happens unconsciously.
• The brain dissects the object, analyzes the various parts
separately, and then produces what appears to be a unified
perception of the whole.
-Anatomy of the visual system
• Retina: light sensitive surface at the back of the eye consisting of
neurons and photoreceptor cells.
-Structure of the eye:
• The cornea and lens of the eye focus light rays to project a
backward, inverted image on the receptive surface, the retina.
• The optic nerve conveys information from the eye o the brain.
• The fovea is the region of best vision and is characterized by the
densest distribution of photoreceptor cells..
• The region in the eye where the blood vessels enter ad the axons
of the ganglion cells leave is called the optic disc and has no
receptors and thus forms a blind spot.
• Convert light energy into chemical energy and then into neural
• Rods: longer and cylindrically shaped at one end, more
numerous than cones, and are more sensitive to dim light. They are used mainly for night vision.
• Cones: shorter and have a tapered end, responsive to bright
light. They are responsible for color vision and our ability to see
fine detail.(have three different pigment types)
• The fovea only has cones, but in lower density at either side-
vision is not so sharp at edges of visual field.
-Retinal Neuron Types
• Retinal ganglion cells: neural cells of the retina that give rise to
the optic nerve. The axons of the ganglion cells collect in a
bundle at the optic disc and leavethe eye to form the optic
o M-Cells: larger and receive their input primarily from rods
and are sensitive to light but not to color. Found
throughout the retina including the periphery where we are
sensitive to movement but not color.
o P-Cells: smaller and receive their input primarily from
cones and are sensitive to color. Found largely in the
• Optic nerves: one exiting from each eye, they are formed by the
axons of ganglion cells leaving the retina. Just before entering
the brain they partly cross forming the optic chiasm.
• The left half of each optic nerve goes to the left side of the brain,
and the right halves go to the brain’s right side.
• The nasal or medial path cross to the opposite side, while the
lateral or temporal go straight back on the same side.
• Geniculostriate system: after entering the brain the axons of the
ganglion cells separate, forming two distinct pathways. This one
goes from the retinal to the LGN of the thalamus and then to
layer IV of the primary visual cortex in the occipital lobes.
• Tectopulvinar system: retina to the superior colliculus to the
Geniculostriate Pathway (detailed)
• Retinal ganglion cell fibers from the two eyes distribute their
connections to the two LGN of the thalamus. Fibers from the left
half of each retina go to the left LGN and those from the right
half go to the right LGN.
• Each LGN has six layers, and projections from two eyes go to
different layers- layers 2,3,5 receive ipsilateral fibers and 1,4,6
receive contralateral fibers.
o This serves to combine the information from the two eyes
and segregate the information from the P and M ganglion
cells. • P-cells go to layers 3-6 and M cells go to layers 1-2.
• Layer IV of the visual cortex has sublayers, IVCa and IVCB.
o IVCa-layers 1 and 2
o IVCb-layers 3-6
• Composed of at least six different visual regions, V1-V6. V1 is
the primary visual cortex or the striate cortex.
• Region V1: Neurons in the blobs take part in color perception,
whereas neurons in the interblobs participate in form and motion
• Region V2: thick stripes receive input from the movement
sensitive neurons in region V1, thin stripes receive input from
V1’s color sensitive neurons, pale ones receive input from V1’s
form sensitive neurons.
Dorsal and Ventral Visual Streams
• Two pathways that originate in the striate cortex. Pathway to
the temporal lobe is the ventral stream, to the parietal lobe is
the dorsal stream.
• Dorsal: goes to the parietal lobe ad controls visual action
• Ventral: goes to temporal lobe, controls object recognition.
-Location in the Visual World
• The coding of location begins in the retina and is maintained
throughout all the visual pathways.
• Visual field: region of the visual world that is seen by the eyes,
can be divided into two halves to form the left and right visual
• The input from the right field goes to left hemisphere and vice
-Coding Location in the Retina
• Receptive field: the patch of the retina in which each ganglion
cell responds if stimulated. It is a region of the retina on which it
is possible to influence that cell’s firing, it represents the outer
world as seen by a single cell.
-Location in the LGN and Cortical Region V1
• The information from a receptive field retains its spatial relation
when it is sent to the lateral geniculate nucleus.
• The receptive fields of many retinal ganglion cells combine to
form the receptive field of a single LGN cell. The receptive fields
of many LGn cells combine to form the receptive field of a single
-The Visual Corpus Callosum • Binds the two sides of the visual field at the midline. Much of the
frontal lobes have callosal connections but the occipital lobes
have almost none.
• When visually responsive neurons encounter a particular
stimulus in their visual fields, they may show either excitation or
-Processing in the Retinal Ganglion Cells
• Cells in retina do not see shapes, they are constructed by
processes in the cortex from the information ganglion cells pass
• On center cell: spot of light falling in the central circle excites
and spot of light falling in periphery inhibits. Light across the
entire receptive field causes a weak increase.
• Off center: the opposite. Luminance contrast: the ability of the
ganglion cell to tell the brain about the amount of light hitting a
certain spot on the retina compared with the average amount of
light falling on the surrounding retinal region.
• Info transmitted from ganglion cells emphasize regions
containing differences in luminance. Areas with differences in
luminance are found along edges.
-Processing in the Primary Visual Cortex
• Cells are maximally excited by bars of light oriented in a
particular direction rather than by spots of light-orientation
• Simple visual cortex cells: respond to a bar of light in a particular
orientation such as horizontal or oblique. The position of the bar
in the visual field is important because the