Final Review Session Neural Correlates of Visual Awareness Mirror Neurons

Neural Correlates of Visual Awareness Difficulties of answering this: What is it about our brains that makes us conscious? Has led to study of this: What are the neural correlates of consciousness (NCC)?

Neural Correlates of Visual Awareness Key points: Not all neural activity results in consciousness Correlates with activity in the ventral pathway The mechanism that causes consciousness has not been identified But consciousness is probably distributed, rather than having one locus

Neural Correlates of Visual Awareness Double dissociation between V5  akinetopsia (localization) V4  achromatopsia (object recognition) Ventral “What” Pathway Dorsal “Where” Pathway V5

Neural Correlates of Visual Awareness Pohl (1973): Landmark task Impaired with parietal lesion (dorsal, “where” pathway)

Neural Correlates of Visual Awareness Pohl (1973): Object task Impaired with temporal lesion (ventral, “what” pathway)

Neural Correlates of Visual Awareness Agnosia Lesion of the inferior temporal cortex (particularly on the left) may result in disorders of memory for people and things Explicit (conscious) decisions about object features are disrupted

Neural Correlates of Visual Awareness Goodale & Milner – Patient DF agnosia (inferior temporal lobe lesion  ventral pathway) Patient could not indicate the orientation of a slot  conscious Patient could move her hand appropriately to interact with the slot  not conscious

Neural Correlates of Visual Awareness Blindsight Scotoma: blind area of visual field Individual denies being able to see anything in the scotoma, but eye movements to stimuli in that part of the field better than chance

Retinocollicular Pathway independently mediates orienting Rafal et al. (1990) Subjects with blindsight move eyes to fixate a peripheral target in two different conditions: – target alone – accompanied by distractor Neural Correlates of Visual Awareness

Rafal et al. (1990)  Subjects were slower when presented with a distracting stimulus in the scotoma (359 ms vs. 500 ms) Blindsight patients have since been shown to posses a surprising range of “residual” visual abilities – better than chance at detection and discrimination of some visual features such as direction of motion Retinocollicular Pathway independently mediates orienting Neural Correlates of Visual Awareness

Recall that the feed-forward sweep is not a single wave of information and that it doesn’t only go through V1 Retinocollicular Pathway independently mediates orienting Neural Correlates of Visual Awareness In particular, MT seems to get very early and direct input Information represented in dorsal pathway guides behaviour but doesn’t support awareness

Binocular Rivalry Important in the study of consciousness as visual perception alternates between aware and unaware in ways that can be correlated with neural events Neural Correlates of Visual Awareness Left Eye Right Eye

Binocular Rivalry Percept alternates randomly (not regularly) between dominance and suppression - on the order of seconds – Several features tend to increase the time one image is dominant (visible) Higher contrast Brighter Motion Neural Correlates of Visual Awareness

Neural Correlates of Rivalry Tong et al. (1998) Used fMRI in conjunction with 2 alternating types of stimuli: faces  fusiform face area and buildings  parahippocampal place area Neural Correlates of Visual Awareness

Neural Correlates of Rivalry Tong et al. (1998) Present faces to one eye and buildings to another Neural Correlates of Visual Awareness Activation between areas “flips” as awareness switches between the two stimuli

Neurophysiology of Rivalry Monkey is trained to indicate which of two images it is perceiving (by pressing a lever) One stimulus contains features to which a given recorded neuron is “tuned”, the other does not Where do changes occur relative to states of suppression and dominance? Neural Correlates of Visual Awareness

Neurophysiology of Rivalry Where do changes occur relative to states of suppression and dominance?  LGN  V1, V4, V5 (small changes when preferred stimulus is dominant, but never stop firing altogether  Inferior Temporal Cortex (Ventral Pathway) Neural Correlates of Visual Awareness

Questions 1)Where is the function of consciousness localized in the brain?

Questions 1)Where is the function of consciousness localized in the brain? “Consciousness is probably distributed, rather than having one locus” However, if we are talking about the neural correlates of visual awareness, the ventral pathway seems to be involved somehow (Pohl, 1973; Goodale & Milner; Rafal et al, 1990).

Questions 2) How does blindsight contribute to our understanding of the neural correlates of visual awareness? Note: Could also ask how binocular rivalry contributes to our understanding of visual awareness.

Questions 2) How does blindsight contribute to our understanding of the neural correlates of visual awareness? Individuals with blindsight have a lesions involving the retinostriate pathway. They orient to stimuli in the scotoma (better than chance) but are not aware of the stimuli. Therefore, it suggests that the retinostriate pathway is implicated in visual awareness.

Questions 3) How does the double dissociation between the functions of object recognition and localization contribute to our understanding of the visual awareness?

Questions 3) How does the double dissociation between the functions of object recognition and localization contribute to our understanding of the visual awareness? Object recognition is attributable to the ventral “what” pathway and localization is attributable to the dorsal “where” pathway. Thus, the double dissociation allows us to examine how the two distinct pathways may be involved in visual awareness. Note: Keep in mind that not all neural activity is “sufficient to cause awareness.”

Questions 4) a) Describe the Tong et al. (1998) experiment. b) Explain why it is important in our understanding of visual awareness.

Questions 4) a) Describe the Tong et al. (1998) experiment. Demonstrates that metabolic techniques such as PET and fMRI permit us to see correlates of awareness.

Questions 4) b) Explain why it is important in our understanding of visual awareness. Activation between the fusiform face area and the parahippocampal place area “flips” as the subject’s awareness switches between the two stimuli. Thus, visual awareness correlates with the region of cortical activation. What mediates this process is unclear from this experiment. [Aside: The neurophysiology experiment with monkeys suggests the inferior temporal lobe is somehow involved.]

Found in regions immediately adjacent to areas that are part of the frontoparietal action planning network Mirror Neurons

Same motor properties Different sensory properties – These cells when monkey sees another monkey (or a person!) perform actions relative to objects Strictly congruent (1/3) and broadly congruent types (2/3) Mirror neurons represent abstract actions and goals Mirror Neurons

fMRI studies in humans have found evidence for two brain regions associated with imitative actions Task 1: watch action Task 2: perform action Task 3: imitate action Mirror Neurons

Based on work with monkeys, it was presumed that mirror neuron areas would exhibit a specific pattern of BOLD response: Task 1 < Task 2 < Task 3 Two regions exhibited such a response Mirror Neurons Inferior parietal Premotor cortex (Broca’s on left)

fMRI data shows that BOLD signal in MNS during viewing and imitating emotional expressions is negatively correlated with scores on social scales (severity of Autism Spectrum Disorder) Mirror Neurons

Questions 1) a) What are mirror neurons? b) Describe the difference between strictly congruent and broadly congruent subtypes. c) Where are they located?

Questions 1) a) What are mirror neurons? Same motor properties as surrounding cells. Sensory properties are different: tuned to “fire” when actions relative to objects are merely observed or implied.

Questions 1) b) Describe the difference between strictly congruent and broadly congruent subtypes. Strictly congruent- fire in response to a specific movement (e.g. using two fingers to pick up an object) Broadly congruent- fire in response to any movement that accomplishes the same goal

Questions 1) c) Where are they located? Cells adjacent to the frontoparietal action planning network In the premotor cortex and inferior parietal cortex.