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Regardless of whether one favours a cognitive, feedback, or central theory of emotion, the common feature is that there must be some mechanism for computing the affective significance of stimuli.
Emotional versus propositional / mundane information
Detection of information that is goal relevant, of biological / adaptive significance… relevant to one personally in terms of harm or benefit
In 1937, Kluver and Bucy identified that animals that had large lesions to their temporal lobe produced a behavioural syndrome that is best characterized as ‘psychic blindness’: An inability to apprehend the motivational or emotional significance of stimuli or events in their environment although they were capable of processing the sensory properties of stimuli.
No manifestation of fear in situations that would normally be expected to elicit fear.
Hyper-orality– any object… even ate their own feces
Sexual deviant behaviour: attempted to copulate with animals who were members of other species
Weizkrantz later showed that lesions isolate to the amygdaloid complex deep in the temporal lobe are the relevant structures, that, when damaged result in the behavioural manifestations of K-B syndrome.
Thus the amygdala assigns emotional significance
Amygdala is the neural instantiation of the psychological construct of appraisal
Electrophysiological recordings of cells in the amygdala respond preferentially to the affective significance of stimuli
Less sensitive to physical features.
Receives projections from exteroceptive sensory cortex involved in the processing of visual, auditory, gustatory and olfactory stimuli.
The ‘Low Road’
Traditionally, it was thought that the thalamic nuclei projected only to respective primary sensory cortex.
More recently it has been discovered that distinct groups of cells within the thalamus project to the lateral nucleus of the amygdala.
These thalamo-amygdala projections are sufficient for the conditioning of a fear response, as they are seen even in decorticate animals.
Conditioned Emotional Learning (fear)
A form of classical conditioning
UCS (biologically relevant) elicits an UCR adaptive / functional
UCS (foot shock) is paired with an tone (CS)
After several pairings, the CS is able to elicit a conditioned response (CR; or conditioned emotional response: CER) similar to the UCR (originally associated with the UCS).
CER = increase in HR and other features of autonomic arousal, specific defensive behaviours (freezing; startle).
LeDoux’s Research Program / Rationale
Lesions to auditory cortex (NO). Even decerebrate rats can manifest CEL.
Lesions to auditory thalamus /MGN (YES)
Injection of tracers HRP to determine the projections of the thalamus.
Projections to Amygdala among other subcortical neuroanatomical structures, including the striatum, thalamus, and hypothalamus.
Lesions to amygdala disrupt CEL, but not lesions to any of these other regions.
Central nucleus (CN) is the major output structure of the amygdala. Projects to:
Central grey: controls freezing response
Reticulopontis caudalis: startle response
Lateral hypothalamus: blood pressure
Paraventricular Nucleus: stress hormones
Lesions to each of these pathways from the amygdala eradicates the behaviour controlled by that region.
Thalamo-amygdala system sufficient for CEL
However, thalamo-cortical-amygdala and thalamo-amygdala pathways converge in the lateral amygdala and are interchangeable as CS transmission routes.
The ‘High Road’
For discriminated tones, the thalamo-cortical-amygdala pathway is necessary
Otherwise, failure to inhibit responses to the CS that is unrelated to the UCS.
Higher processing structures are involved in CEL for increasingly more complex stimuli that serve as CS.
e.g., lesions to the hippocampus do not interfere with CEL to simple or discriminated tones, but disrupt conditioning to contextual stimuli (e.g., the room in which the foot-shock took place).
Low versus High road pathways
The amygdala receives input from a variety of neuroanatomical structures that vary in the complexity of their cognitive operations
Thalamus: for crude stimulus information. Fewer synapses, therefore quicker… makes up in speed what it lacks in processing quality (‘the quick vs. the dead’)
Also prepares the amygdala for the arrival of more complex stimulus information from the cortex
amygdala already informed of the modality and crude stimulus properties.
Hippocampus: Sensory information is integrated in various association cortices before reaching the hippocampus, relative to the amygdala
Projections from the hippocampus may allow the amygdala to evaluate affective significance of information processed by the hippocampus:
i.e., contextual, relational, or memory-based
also, emotion can be generated by thoughts or memories… e.g., remember what you forgot to do.
CS-1 and UCS are paired
CS-2 is introduced… but does not acquire CEL
The pairing of the first CS with the UCS appears to block the conditioning of the second CS
Hippocampus lesions: conditioning occurs to both stimuli. The animal is no longer able to filter out irrelevant / redundant stimuli.
These animals are more likely to develop stress-related ulcers.
To the extent to which coping is a cognitive process, lesions of the hippocampus impair the modulation of amygdala activity
This is a central feature of many forms of psychotherapy (using cognition to modulate emotion)
Infantile amnesia: we have little conscious / episodic / declarative memory of the first two years of life (what is your first memory?)
Jacobs and Nadel (1985) argue that the inability to recall memories in early childhood reflects the delayed maturation of the hippocampus (18 to 36 months in humans, while amygdala is mostly developed in embryo).
Memory codes laid down prior to the development of the hippocampus use codes that are indecipherable to the hippocampus or linguistic / symbolic systems.
In contrast, most of the amygdala’s neurons are fully developed earlier in embryonic stages and are fully present at birth.
Thus, the amygdala may be particularly important in early learning and the establishment of affective memories prior to the maturation of cognitive functions mediated by the hippocampus.
Parallel between infantile memories and fear/phobia learning in adults in which stress hormones are released which interfere with the development of long term potentiation in the hippocampus and thus the establishment of memory traces.
How do the different routes for transmission of information to the amygdala (which generates emotional responses and is the structure responsible for emotional learning) help to resolve the dispute between Zajonc and Lazarus?
The amygdala is reciprocally connected to many of the structures previous mentioned that are involved in higher cognitive processing. What is the implication of this observation for other theories we have studied in the class so far?
Lateralization of Emotion
Perception, Expression, Experience.
Emotional perception is represented more in the posterior areas of the cerebral cortex, and expression and experience more in the anterior regions.
With that said, there are two basic theories of the laterality of emotional processes within the brain: One that assumes right hemisphere superiority for all emotional processing, and one that divides hemispheric specialization according to valence.
Perception of emotional expressions
The right hemisphere of the brain seems to be specialized for emotional expression: in most right handed individuals facial expressions are more salient on the left side of the face.
Patients with RH damage have difficulty recognizing facial expressions of emotion
Split Brain patients: sever the corpus callosum: can recognize emotionally salient events when presented to the LVF. E.g. Gazzaniga (1988) showed SB patients a film of a person being thrown on to a fire to their LVF. The patient could not describe what it was they saw, but could not verbally describe what it was they saw since language depends on LH function. However, the patient reported feeling scared and jumpy and nervous, which they attributed to the presence of the experimenter or the room.
The information from the visual processing of the upsetting scene did not reach the LH, but the processing of the fear-related stimulus probably involved limbic system structures that are below the level of the severed callosum.
Limbic system and the right hemisphere do not operate in terms of symbolic linguistic representation, yet cross-hemispheric connections do exist (e.g., anterior commissure)
Thus, information about the general emotional tone of the scene was conveyed to the left hemisphere, which could verbalize a general feeling of anxiety/uneasiness.
This example is interesting given our previous readings about cognitive labeling theories of emotion: The experience set up an evaluative need that was then attributed to situational cues (the room, the experimenter).
Right Hemisphere => perceiving emotion
When normals are shown a ‘Chimeric face’, they most often report that the face with the lip upturned on the right side (left from the viewer’s perspective) looks more happy, and the face with right lip turned downwards looks more sad.
When pictures are flashed briefly with unilateral visual field presentation, recognition of emotional expressions is better for faces presented in the left visual field.
Tucker & Frederick (1989) have noted that the right cerebral cortex has closer connections with the amygdala than the left cerebral cortex.
The Valence hypothesis: Emotional experience is lateralized in the cerebral cortex
Left hemisphere is specialized for the experience of positive emotion, and the right hemisphere is specialized for the experience of negative emotion.
Davidson’s variation of the Valence hypothesis posits that approach / withdrawal tendencies are a precursor to the laterality of emotional experience by valence.
Lateralization of responses is thought to represent an effective means of reducing competitive interactions between these two fundamental response processes.
LeDoux’s Research Program / Rationale
Evidence from brain damaged patients:
Left frontal lesions are associated with a catastrophic/depressive reaction
Right frontal lesions are associated with an indifferent/euphoric reaction
Robinson (1984): patients who suffered left hemisphere strokes were more likely to suffer from depression than those with right hemisphere strokes.
Effect stronger when lesion was closer to the frontal pole
Studies of the behaviour of brain damaged individuals thought to reflect the functioning of intact hemisphere.
Previous failures to find effects of lesion side may be the result of not differentiating between: anterior versus posterior; emotional perception, expression, and experience; or to take into account a stress-diathesis model (lesion represents vulnerability)
Depressed individuals show decrease in left frontal activation, as measured by EEG
Left frontal hypoactivation and hypometabolism in depressed individuals as measured by PET and SPECT especially in the anterior cingulate gyrus
Bench et al. (1996) showed that this asymmetry resolved upon successful antidepressant therapy
Wada Test: Unilateral injection of Sodium Amytal into the carotid artery: functional hemispherectomy
Preoperative assessment of language and memory function in individuals who are candidates to receive psychosurgery for intractable temporal lobe epilepsy
Left side injection = anesthetization of the left hemisphere, resulting in observation of the function of the right hemisphere… catastrophic depressive reaction characterized by crying, pessimism, worries of the future, and guilt.
Right side injection = euphoric reaction characterized by a lack of apprehension, smiling, laughing, optimism, and a sense of well-being.
Consistent with brain-damage results.
Evidence from non-clinical populations
Diamond and colleagues (1976) used special contact lenses to present different types of emotionally salient films: pleasant, humorous, unpleasant, or horrific.
Films presented to the right hemisphere (LVF) were rated as more horrific and unpleasant than the same films presented to the left hemisphere (RVF).
Wittling and Pfluger (1993) found that right hemisphere presentation of unpleasant films was related to an increase in salivary cortisol levels (stress response).
Davidson et al. (1990) had participants watch positive and negative film clips and took unobtrusive video recordings of their facial expressions.
Expressions of disgust, were associated with greater right frontal activation, while expressions of happiness were associated with greater left frontal activation.
Also, remember the results from the assigned reading (Duchenne smile paper): Duchenne smiling was associated with more left-sided anterior temporal and parietal activation than other smiles. Other smiles were associated with more right frontal activity than baseline.
Affective style: Emotionality trait
Personality variable (trait) that results in a propensity to react in positive or negative ways to stimuli and events
Tomarken et al. (1992) found that subjects who sustained an asymmetric pattern of activation over a three-week period reported increased generalized positive affect, and less negative affect compared to those with stable right anterior activity
Wheeler et al. (1993) showed that patterns of sustained asymmetrical cerebral activation (as measured by EEG) predicted reactions to emotionally evocative films.
Greater right frontal activation was associated with reports of more negative affect in response to the negative emotional film clips compared to subjects with stable left frontal activation who reported more intense positive affect to positive film clips.
Unilateral Hemispheric Activation
Schiff and Lamon (1989) showed that contraction of the right hand of face resulted in feelings of aggressive well-being, while contractions of the left hand or face resulted in more negative emotion, as assessed with a semi-clinical interview.
The sensory and motor fibers from the hand and lower 2/3 of the face connect to the contralateral cerebral hemisphere, and thus these results are consistent with the valence hypothesis.
Mainly zygomaticus major contraction. Is this a problem? Why?
Subsequent research showed this effect to be apparent with the interpretation of ambiguous stimuli from the TAT, from judgment of racial stereotypes, transient unilateral pain, chronic unilateral pain, and behavioural persistence.
A PET investigation showed activation in the contralateral anterior cingulate gyrus two minutes following the cessation of a set of unilateral contractions in an area associated with the motivational and emotional consequences of pain and vibrotactile stimulation.
Mechanism may be the spreading of activation from these regions to those associated with biasing emotional functions (i.e., attention). This is consistent with the observation that the effects of the contractions are usually found with implicit or ambiguous stimuli, not self-report.