L4

1. Explain the fMRI, PET and EEG techniques, highlighting their advantages and disadvantages.

1. Explain the fMRI, PET and EEG techniques, highlighting their advantages and disadvantages.

Positron Emission Tomography (PET) : Uses a synthetic radiotracer that reacts with tissue and produces a signal that can be detected • Wherever the radiotracer goes, there will be a signal

Two general purposes: 

• Measuring metabolic activity 

• Characterizing distribution of specific substances

Measuring activity w/PET: 

• If the radiotracer is similar to glucose (such as Fluorodeoxyglucose ( 18F)), it will be distributed in the same way (i.e. to active neurons) 

• Signal differences between brain regions reflect differences in glucose demands (+ neuronal activity) 

Decent spatial resolution 

• Better than EEG but worse than MRI 

• Poor temporal resolution 

• Difficult to resolve rapid changes in neural activity 

• Due to its resolution issues, PET is no longer preferred as a structural/functional measure in psychology 

• It does have other very important uses in neuroscience and medicine (but you won’t need to know these)

Basis of the fMRI signal • Active neurons use glucose + oxygen • After blood delivers oxygen, it becomes deoxygenated • If you knew the brain areas where there was a change in blood oxygenation, you would know the brain areas that are changing in activity

fMRI – Summary 

• Great spatial resolution (great for studying brain structure) 

• Best out of techniques we have covered today 

• Can be ‘paired’ w/other techniques (e.g. PET) 

• Decent temporal resolution 

• Better than PET (arguably), not as good as EEG or MEG 

• Lag of seconds between activity and signal is still evident 

• Popular technique for cognitive neuroscience

Electroencephalography (EEG) Measures electrical activity in specific brain regions. Useful in studies of arousal, consciousness + epilepsy. 3 Electrodes are placed above a small amount of neurons.

EEG + ERP – Summary 

• Great temporal resolution (biggest advantage) 

• Millisecond scale 

• Great for measuring rapid changes in arousal/consciousness (regular EEG) and rapid cognitive processes (ERP) 

• Poor spatial resolution (biggest disadvantage) 

• Difficult to determine which specific areas are active 

• Deeper brain areas cannot be measured

1. Discuss the strengths and weaknesses of lesion studies. 

On case studies… 

• Lesions rarely specific (many brain areas involved) • Behavioral impairments could be due to damage in any one of these areas 

• Other behaviors could be impaired but not measured • Effects of brain lesions could be more extensive than thought 

• Cases are very rare (often N = 1) 

• Is it repeatable? Or was it chance?

 • Difficult to make a conclusive argument based on them 

• Not experimental, no control for other variables (e.g. individual differences, life history)

1. Comment on the general layout of sensory pathways, being sure to emphasize the major cortical area for each sense.

Explain the Young-Helmholtz trichromatic and Opponent-process color theory.

Trichromatic Color Theory • Also called Young-Helmholtz Theory • Every color is a combination of three independent color signals (and perhaps the activity of three cones) • Analogy: Color Slider in Imaging Software

Opponent Process Color Theory • Processing of signals in pairs, contrasting color signals interact (Blue v. Yellow, Red v. Green, Black v. White) Explains after images

1. Be familiar with all the terminology of stimulus detection. Explain response bias. 

1. Be familiar with all the terminology of stimulus detection. Explain response bias. 

1. Define absolute threshold. What is a subliminal stimulus? 

Absolute threshold refers to the lowest stimulus intensity (in units) at which we can correctly detect the stimulus >50% of the time (i.e. above chance) 

• Stimuli below this threshold are not detectable (i.e. beneath conscious awareness), but that does not mean they are unimportant

Subliminal stimulation is sensory stimulation that is below a person's threshold for perception. It can't be seen by the naked eye or consciously heard.

1. Explain the just noticeable difference (JND), also called the difference threshold. How is JND related to stimulus intensity? What is the Weber-Fechner Law? 

Just Noticeable Difference (JND) • Also termed the difference threshold • The point (in stimulus units) at which you can just barely discriminate a change in a stimulus • ○C for temperature discriminations • kg for weight discriminations • For example, if you’re trying to discriminate weights and JND = 4 kg… • You could distinguish weights differing by ≥ 4 kg • You could distinguish 1 kg from 5 kg • You could NOT distinguish 1 kg from 3 kg

Weber-Fechner Law 

• JND is generally proportional to stimulus intensity 

• This law attempts to describe our ability to detect changes in the property of a stimulus • I/I = K

• The slope, K, is a constant 

• As K is constant, we can expect that the JND (I) will increase any time stimulus intensity (I) increases. 

According to the theory, which task is easier: 

A.Discriminating a 55kg weight from a 50kg weight 

B. Discriminating a 6kg weight from a 1kg weight 

1. Why might sleep be useful? 

Sleep helps maintain cognitive skills, such as attention, learning, and memory

1. Define the stages of sleep. How might we distinguish them?

Sleep stages 

Stage NREM1 

Stage NREM2 

Stage NREM3/4 

REM 

Sleep stages are traditionally measured in a lab using an electroencephalogram to detect brain activity along with other systems to monitor eye and muscle activity. These stages are determined based on an analysis of brain activity during sleep, which shows distinct patterns that characterize each stage.

Frequency ranges 

Beta: >13 Hz

 Alpha: 7-13 Hz 

Theta: 4-7 Hz 

Delta: 1-4 Hz

1. What are the three theories of dreaming?

• Dream Protection Theory 

Sexual + aggressive instincts are transformed into symbols that represent wish fulfillment; interpretation required 

• Evolutionary Theory 

Dreams about threats to reproductive success, plan solutions 

• Activation-Synthesis Theory 

 Dreams are an attempt by the brain to interpret random activity

1. Explain hypnosis. What factors are correlated with sensitivity to hypnosis?

Trance-like state, generally induced 

• ~20% highly responsive, equal amount unresponsive 

• Best candidates: 

• willing/eager • open to new experiences • able to focus their attention 

• capable of fantasy • show conformity, obedience and suggestibility

1. What is meditation? What disorders might meditation help treat?

An activity in which an individual either trains the mind and/or induces an altered state of consciousness 

• Meditation is widely practiced and has shaped culture, religion and medicine • ~8% of adults have meditated (1.6% of children)1 

• Certain meditation styles – such as mindfulness meditation – may help treat anxiety, depression and chronic pain disorders2

1. Describe near-death experiences by highlighting their characteristics, causes and consequences.

Near Death Experiences (NDEs)

Experience associated with death or impending death 

• Though NDEs vary between individuals of different backgrounds, particular characteristics are often present, usually in a certain order 

• May be studied using the Greyson NDE scale 

• Aspects of NDEs can be brought about with drugs (ketamine, DMT, opioids), brain stimulation or hypoxia • Many models, cause unclear