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Chapter 4: The Organized Brain

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1 Chapter 4: The Organized Brain

2 Overview of Questions How can brain damage affect a person’s perception? Are there separate brain areas that determine our perception of different qualities? How has the operation of our visual system been shaped by evolution and by our day-to-day experiences?

3 Lateral Geniculate Nucleus of the Thalamus

4 Maps: Representing Spatial Layout
Retinotopic map - each place on the retina corresponds to a place on the LGN Determining retinotopic maps - record from neurons with an electrode that penetrates the LGN obliquely LGN has 6 layers Stimulating receptive fields on the retina shows the location of the corresponding neuron in the LGN LGN - Lateral Geniculate Nucleus Important to note that the receptive field for ANY neuron in the system is at the receptor cells for that modality -- for vision, that will always be the retina. Students tend to forget this and get confused later.

5 Lateral Geniculate Nucleus

6 Retinotopic mapping of neurons in the LGN.

7 Cortex shows retinotopic map too
The Map on the Cortex Cortex shows retinotopic map too Electrodes recording from a cat’s visual cortex shows: Receptive fields on the retina that overlap also overlap in the cortex This pattern is seen using an oblique penetration of the cortex It might be helpful here to explain how the Hubel and Wiesel experiment works. Stimuli are shown on specific points on the retina to find the stimulus and the receptive field that stimulates a neuron in the cortex that is being monitored by an electrode. This is also a good place to discuss ethics in the use of the animals for research, if the instructor desires to do so.

8 Retinotopic mapping of neurons in the cortex.

9 The Map on the Cortex - continued
Cortical magnification factor Fovea has more cortical space than expected Fovea accounts for .01% of retina Signals from fovea account for 8% to 10% of the visual cortex This provides extra processing for high-acuity tasks How do we know this stuff?

10 Brain Imaging Techniques
Positron emission tomography (PET) Person is injected with a harmless radioactive tracer Tracer moves through bloodstream Monitoring the radioactivity measures blood flow Changes in blood flow show changes in brain activity The instructor can connect this section on brain imaging techniques by explaining to the students that these methods have been used to provide evidence for the magnification factor for the fovea found in the visual cortex.

11 The subtraction technique

12 Brain Imaging Techniques - continued
Functional magnetic resonance imaging (fMRI) measures blood flow by: Hemoglobin carries oxygen and contains a ferrous molecule that is magnetic Brain activity takes up oxygen, which makes the hemoglobin more magnetic fMRI determines activity of areas of the brain by detecting changes in magnetic response of hemoglobin Subtraction technique is used like in PET

13 Purple and teal areas show the extent of stimuli that were presented while a person was in an fMRI scanner. (b) Purple and teal indicates areas of the brain activated by the stimulation in (a).

14 Organization in Columns
LGN receives signals for right and left eyes Layers 2, 3, and 5 receive input from the ipsilateral eye Layers 1, 4, and 6 receive input from the contralateral eye Electrodes inserted perpendicular to the surface show that receptive fields along the track are in the same location in the retina Note: make sure to remind students that there is an LGN in both hemispheres. You can also tell them they can use the prefix “contra” as a memory aid for the term contralateral. Finally, this is a good place to point out that the separation of the input from the right and left eye is the first place that brain compares the slightly different images from each eye which begin the process of 3-D vision.

15 Cross section of the LGN showing layers.

16 Organization in Columns - continued
Visual cortex shows: Location columns Receptive fields at the same location on the retina are within a column Orientation columns Neurons within columns fire maximally to the same orientation of stimuli Adjacent columns change preference in an orderly fashion 1 millimeter across the cortex represents entire range of orientation

17 Figure 4.9 When an electrode penetrates the cortex perpendicularly, the receptive fields of the neurons encountered along this track overlap. The receptive field recorded at each numbered position along the electrode track is indicated by a correspondingly numbered square.

18 All of the cortical neurons encountered along track A respond best to horizontal bars (indicated by the red lines cutting across the electrode track.) All of the neurons along track B respond best to bars oriented at 45 degrees.

19 Organization in Columns - continued
Visual cortex shows (cont.) Ocular dominance columns Neurons in the cortex respond preferentially to one eye Neurons with the same preference are organized into columns The columns alternate in a left-right pattern every .25 to .50 mm across the cortex

20 This slide can be used to talk about the entire process using this image as an example for how incoming stimulation is organized beginning with the neurons in the retina, through the LGN and into the cortex. The text has material on this that can be added to the lecture. Figure 4.11 (a) How a peppermint stick creates an image on the retina and a pattern of activation on the cortex. (b) How a long peppermint stick would activate a number of different orientation columns in the cortex.

21 Lesioning or Ablation Experiments
An animal is trained to indicate perceptual capacities A specific part of the brain is removed or destroyed The animal is retrained to determine which perceptual abilities remain The results reveal which portions of the brain are responsible for specific behaviors

22 What and Where Pathways
Ungerleider and Mishkin (1983) Object discrimination problem Monkey is shown an object Then presented with two choice task Reward given for detecting the target Landmark discrimination problem Monkey is trained to pick the food well next to a cylinder

23 What and Where Pathways - continued
Ungerleider and Mishkin (cont.) Using ablation, part of the parietal lobe was removed from half the monkeys and part of the temporal lobe was removed from the other half Retesting the monkeys showed that: Removal of temporal lobe tissue resulted in problems with the landmark discrimination task - What pathway (I see it, but don’t know where it is) Removal of parietal lobe tissue resulted in problems with the object discrimination task - Where pathway (I know where it is, but I don’t know what it is)

24 The monkey cortex, showing the what, or ventral pathway from the occipital lobe to the temporal lobe, and the where, or dorsal pathway from the occipital lobe to the parietal lobe.

25 What and Where Pathways - continued
What pathway also called doral pathway Where pathway also called ventral pathway Both pathways originate in retina Ventral pathway begins in small or medium ganglion cells Called P-cells Axons synapse in layers 3, 4, 5, & 6 of LGN Called parvocellular layers

26 What and Where Pathways - continued
Dorsal pathway begins in large ganglion cells Called M-cells Axons synapse in layers 1 & 2 of LGN Called magnocellular layers Ablation research with monkeys shows: Parvo channels send color, texture, shape and depth information Magno channels send motion information

27 Make sure to note here that the even though the pathways have different functions, they have interconnections, and there is a feedback loop for information within both systems. The dorsal and ventral streams in the cortex originate with the magno and parvo ganglion cells and the magno and parvo layers of the LGN. The red arrow represents connections between the streams. The dashed blue arrows represent feedback - signals that flow “backward.”

28 Retinal ganglion cells and their functions.

29 What and Where Pathways - continued
Where pathway may actually be “How” pathway Dorsal stream shows function for both location and for action Evidence from neuropsychology Single dissociations: two functions involve different mechanisms Double dissociations: two functions involve different mechanisms and operate independently Note the neuropsychology involves the study of the behavioral effects of brain damage.

30 Table 4.2 Double dissociations in TV sets and people.

31 What and How Pathways - Neuropsycholgical Evidence
Behavior of patient D.F. Damage to ventral pathway due to gas leak Not able to match orientation of card with slot But was able to match orientation if she was placing card in a slot Other patients show opposite effects Evidence shows double dissociation between ventral and dorsal pathways This shows explicitly the double dissociation between judging orientation and the coordination of vision and action. It also shows that the how pathway (where pathway) could also be called the action pathway.

32 Figure 4. 16 Performance of D. F
Figure 4.16 Performance of D.F. and a person without brain damage for two tasks: (a) judging the orientation of a slot; and (b) placing a card through the slot. See text for details. (From the Visual Brain in Action by A. D. Milner and M. A. Goodale. Copyright ©1995 by Oxford University Press. Reprinted by permission.)

33 What and How Pathways - Further Evidence
Rod and frame illusion Observers perform two tasks: matching and grasping Matching task involves ventral (what) pathway Grasping task involves dorsal (how) pathway Results show that the frame orientation affects the matching task but not the grasping task

34 Figure 4. 17 (a) Rod and frame illusion
Figure 4.17 (a) Rod and frame illusion. Both small lines are oriented vertically. (b) Matching task and results. (c) Grasping task and results. See text for details.

35 Modularity: Structures for Faces, Places, and Bodies
Module - a brain structure that processes information about specific stimuli Inferotemporal (IT) cortex in monkeys One part responds best to faces while another responds best to heads Results have led to proposal that IT cortex is a form perception module Temporal lobe damage in humans results in prosopagnosia

36 Figure (a) Monkey brain showing location of the inferotemporal cortex (IT) in the lower part of the temporal lobe. (b) Human brain showing location of the fusiform face area (FFA) in the fusiform gyrus, which is located under the temporal lobe.

37 Figure 4.20 Response of a neuron in the IT cortex for which the person’s head is an important part of the stimulus because firing stops when the head is covered. (From “Recognition of Objects and Their Components Parts: Responses of Single Units in the Temporal Cortex of the Macaque,” by E. Washmuth, M. W. Oram, and D. I. Perrett, 1994, Cerebral Cortex, 4, Copyright © 1994 by Oxford University Press.)

38 Modularity: Structures for Faces, Places, and Bodies - continued
Evidence from humans using fMRI and the subtraction technique show: Fusiform face area (FFA) responds best to faces as well as when context implies a face Parahippocampal place area (PPA) responds best to spatial layout Extrastriate body area (EBA) responds best to pictures of full bodies and body parts Note the the EBA does NOT respond to faces.

39 Figure 4. 21 fMRI response of the human fusiform face area
Figure 4.21 fMRI response of the human fusiform face area. Activation occurs when a face is present (E) or is implied (D) but is lower when other stimuli are presented (A,B,C,F). (Reprinted with permission from Cox, D., Meyers, E., Sinha, P. (2004). Contextually evoked object-specific responses in human visual cortex, Science, 304,

40 Evolution and Plasticity: Neural Specialization
Evolution is partially responsible for shaping sensory responses: Newborn monkeys respond to direction of movement and depth of objects Babies prefer looking at pictures of assembled parts of faces Thus “hardwiring” of neurons plays a part in sensory systems

41 Evolution and Plasticity: Neural Specialization - continued
Plasticity of neurons also shapes sensory responses Experience-dependent plasticity in animals Monkeys trained to recognize specific view of unfamiliar object Other views of object showed decline in recognition as object rotated from trained view Neurons in the IT cortex showed maximal response to the trained orientation Note: You can also refer to experiment with kittens raised in vertical only environment that are mentioned in Chapter 3. You can also refer to the stimulus-perception relationship and stimulus physiological relationship demonstrated in this experiment.

42 Figure 4. 23 (a) Stimuli like those used by Logothetis & Pauls (1995)
Figure 4.23 (a) Stimuli like those used by Logothetis & Pauls (1995). (b) Monkey’s ability to recognize the training shape and rotated views of the shape that were not seen during training. (c) Response of neurons in the IT cortex of the trained monkey to the training shape and the rotated shape.

43 Evolution and Plasticity: Neural Specialization - continued
Experience-dependent plasticity in humans Brain imaging experiments show areas that respond best to letters and words fMRI experiments show that training results in areas of the FFA responding best to: Greeble stimuli Cars and birds for experts in these areas

44 Figure 4. 24 (a) Greeble stimuli used by Gauthier
Figure 4.24 (a) Greeble stimuli used by Gauthier. Participants were trained to name each different Greeble. (b) Brain responses to Greebles and faces before and after Greeble training. (a: From Figure 1a, p. 569, from Gauthier, I., Tarr, M. J., Anderson, A. W., Skudlarski, P. L., & Gore, J. C. (1999). Activation of the middle fusiform “face area” increases with experience in recognizing novel objects. Nature Neuroscience, 2, )

45 Figure 4.25 Ways that the brain is organized.
This slide can act as a summary of the information presented so far that pertains to how the visual system is organized and how their are specific response to specific stimuli. This then leads to the material in the next section on how stimuli are coded specifically by neural firing. Figure Ways that the brain is organized.

46 Sensory Code: Representation of Environment
Sensory code - representation of perceived objects through neural firing Specificity coding - specific neurons responding to specific stimuli Leads to the “grandmother cell” hypothesis Recent research shows cells in the hippocampus that respond to concepts such as Halle Berry

47 Figure 4.29 (a) Location of the hippocampus and some of the other structures that were studied by Quiroga and coworkers (2005)

48 Sensory Code: Representation of Environment - continued
Problems with specificity coding: Too many different stimuli to assign specific neurons Most neurons respond to a number of different stimuli Distributed coding - pattern of firing across many neurons codes specific objects Large number of stimuli can be coded by a few neurons

49 Sensory Code: Representation of Environment - continued
Coding can be distributed across many brain areas Monkeys’ IT cortex shows overlap of activation caused by different stimuli fMRI experiments with humans show the same type of effect Thus, although there is specific response within modules, there is also activation across modules for specific stimuli

50 Figure 4.26 How faces could be coded according to (a) specificity coding and (b) distributed coding. The height of the bars indicates the response of neurons 1, 2, and 3 to each stimulus face. See text for explanation.

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