1. BIO 132 Neurophysiology Lecture 38 Rhythms of the Brain

2. An electroencephalogram (EEG) is a measurement of the activity of the brain, recorded from the surface of the scalp. An electroencephalogram (EEG) is a measurement of the activity of the brain, recorded from the surface of the scalp. Recordings made as early as 1875 Recordings made as early as 1875 Setup: Setup: 24 or so electrodes taped to scalp at standard positions 24 or so electrodes taped to scalp at standard positions Output of electrodes amplified Output of electrodes amplified Differences between the charges recorded at each electrode are made and display on a graph versus time. Differences between the charges recorded at each electrode are made and display on a graph versus time. Measurements of individual neurons is not possible from the scalp, but the activity of collections of neurons is possible. Measurements of individual neurons is not possible from the scalp, but the activity of collections of neurons is possible. Electroencephalogram

3. All cortical neurons have the same orientation; dendrites near the surface and axons projecting inward. All cortical neurons have the same orientation; dendrites near the surface and axons projecting inward. Na + entering dendrites during neuronal firing leaves the outside of the dendrites negatively charged. Na + entering dendrites during neuronal firing leaves the outside of the dendrites negatively charged. If enough neurons beneath an electrode are activated at the same time, the resulting electric field they produce can be detected through the tissue of the scalp. If enough neurons beneath an electrode are activated at the same time, the resulting electric field they produce can be detected through the tissue of the scalp. EEG Setup

4. Scalp Skull Dura mater Arachnoid mater Pia mater Cortex Subarachnoid space Pyramidal neuron Axon Dendrites - - - - ++ + + Input from another area Electrode

5. Collective synchronous activity of thousands of neurons are needed to create an EEG wave. Collective synchronous activity of thousands of neurons are needed to create an EEG wave. More synchronous activity leads waves with larger amplitudes and slower frequencies. More synchronous activity leads waves with larger amplitudes and slower frequencies. Less synchronous activity indicates more active brain activity. Less synchronous activity indicates more active brain activity. Waves are categorized into four general types: Waves are categorized into four general types: Alpha – fast and small; awake states Alpha – fast and small; awake states Beta – fast and small; REM states Beta – fast and small; REM states Theta – slow and large; Non-REM states Theta – slow and large; Non-REM states Delta – very slow and large; Non-REM states Delta – very slow and large; Non-REM states EEG Patterns

6. Alpha Beta Theta Delta 05 Time (sec)

7. There are two hypotheses about what underlies EEG rhythms: There are two hypotheses about what underlies EEG rhythms: A. Pacemaker cells (perhaps in the thalamus) have a constant rhythmic output and can influence other brain areas A. Pacemaker cells (perhaps in the thalamus) have a constant rhythmic output and can influence other brain areas Analogy: A conductor waving his baton influences the rhythm of an orchestra Analogy: A conductor waving his baton influences the rhythm of an orchestra B. Connections between neighboring neurons cause collective firing B. Connections between neighboring neurons cause collective firing Analogy: A crowd of people clapping out of synch will cue off each other and begin clapping in synch. Analogy: A crowd of people clapping out of synch will cue off each other and begin clapping in synch. EEG Wave Sources

8. It is unclear if brain waves measured as EEGs serve a useful function or if they are just an artifact of normal brain activity. It is unclear if brain waves measured as EEGs serve a useful function or if they are just an artifact of normal brain activity. One hypothesis is that perhaps the rhythmic waves are used to code information across different brain areas. However, as yet, there is no evidence for this. One hypothesis is that perhaps the rhythmic waves are used to code information across different brain areas. However, as yet, there is no evidence for this. EEG Wave Functions

9. Seizures are caused by massive synchronous activity that spreads. Seizures are caused by massive synchronous activity that spreads. Epilepsy is when repeated occurrences of seizures happen. Epilepsy is when repeated occurrences of seizures happen. Many causes Many causes GABA agonists sometimes useful treatment GABA agonists sometimes useful treatment General seizure – entire cortex involved as synchronous firing spreads all over General seizure – entire cortex involved as synchronous firing spreads all over Symptoms: loss of consciousness, muscles contract, odd sensations Symptoms: loss of consciousness, muscles contract, odd sensations Partial seizure – localized in a brain area Partial seizure – localized in a brain area Symptoms: (depends on location of seizure) limb movements, odd sensations, hallucinations, déjà vu Symptoms: (depends on location of seizure) limb movements, odd sensations, hallucinations, déjà vu Seizures

10. Definition: A readily reversible state of reduced responsiveness and interaction with the environment. Definition: A readily reversible state of reduced responsiveness and interaction with the environment. A full 1/3 of our lives is spent sleeping A full 1/3 of our lives is spent sleeping About 1/12 of our lives is spent dreaming. About 1/12 of our lives is spent dreaming. Sleep is universal among vertebrates (animals with a spine). Sleep is universal among vertebrates (animals with a spine). Sleep has two stages that repeat over an over: REM and non-REM sleep Sleep has two stages that repeat over an over: REM and non-REM sleep Sleep

11. REM sleep: REM sleep: REM stands for “rapid eye movement” REM stands for “rapid eye movement” EEGs are beta waves during this phase, showing that the brain is very active EEGs are beta waves during this phase, showing that the brain is very active Brain is more active (using more O 2 ) than awake states Brain is more active (using more O 2 ) than awake states Paralysis of all muscles except diaphragm (breathing), extra- ocular muscles (eye movement), and muscles of inner ear. Paralysis of all muscles except diaphragm (breathing), extra- ocular muscles (eye movement), and muscles of inner ear. Muscles have no tone (usually muscle spindles maintain some activity of alpha-motor neurons). Muscles have no tone (usually muscle spindles maintain some activity of alpha-motor neurons). Usually an increase in heart rate and respiration (both somewhat irregular) Usually an increase in heart rate and respiration (both somewhat irregular) Temperature control quits Temperature control quits Dreaming occurs 90-95% of the time in the REM stage Dreaming occurs 90-95% of the time in the REM stage REM vs non-REM

12. Non-REM sleep: Non-REM sleep: Slow large EEGs (both theta and delta waves) Slow large EEGs (both theta and delta waves) Decreased muscle tension but no paralysis Decreased muscle tension but no paralysis Increased parasympathetic activity: Increased parasympathetic activity: Decreased H.R., respiration, metabolism and increased digestion Decreased H.R., respiration, metabolism and increased digestion Decreased brain activity (O2 consumption by the brain is decreased) Decreased brain activity (O2 consumption by the brain is decreased) Decreased sensory input to the cortex Decreased sensory input to the cortex REM vs non-REM

13. The brain cycles between non-REM and REM sleep 4-5 times per night. The brain cycles between non-REM and REM sleep 4-5 times per night. Each cycle lasts about 90 minutes and is called an ultradian rhythm. Each cycle lasts about 90 minutes and is called an ultradian rhythm. Each cycle consists of about 60 minutes of non-REM and 30 minutes of REM sleep. Each cycle consists of about 60 minutes of non-REM and 30 minutes of REM sleep. The proportion of the cycle spent in non-REM sleep is greater at the onset of sleep and diminishes as sleep progresses. The proportion of the cycle spent in non-REM sleep is greater at the onset of sleep and diminishes as sleep progresses. Stages of Sleep

14. 11 pm6 am5 am4 am3 am2 am1 ammidnight TIME Awake (alpha) REM (beta) Stage 1 (theta) Stage 2 (theta) Stage 3 (delta) Stage 4 (delta)

15. There is no known function of sleep. There is no known function of sleep. Hypotheses: Hypotheses: Allows time for regeneration Allows time for regeneration Conserves energy Conserves energy Most animals are nocturnal or diurnal to fill a ecological niche Most animals are nocturnal or diurnal to fill a ecological niche Allows time for sensory processing and laying down of memories Allows time for sensory processing and laying down of memories Although it is unknown, sleep must serve some function Although it is unknown, sleep must serve some function Most animals will die if kept from sleeping for too long Most animals will die if kept from sleeping for too long All vertebrates sleep – evolution would have dropped sleep if it didn’t serve a useful function. All vertebrates sleep – evolution would have dropped sleep if it didn’t serve a useful function. Function of Sleep

16. Circadian rhythm – Biological cycle that lasts one day. Circadian rhythm – Biological cycle that lasts one day. Many systems of the body are affected by circadian rhythms (tough to find one that is not). Many systems of the body are affected by circadian rhythms (tough to find one that is not). Circadian Rhythms TIME Sleep Alertness Temp [Growth hormone] blood [Cortisol] blood [K + ] ICF

17. First evidence of circadian rhythms came from the mimosa plant. First evidence of circadian rhythms came from the mimosa plant. Day – leaves are extended; Night – leaves retracted Day – leaves are extended; Night – leaves retracted In 1729 French physicist, Mairan, placed mimosa plants in a dark closet with no possible sunlight exposure and the plants continued to extend and retract leaves on a 24-hour cycle. In 1729 French physicist, Mairan, placed mimosa plants in a dark closet with no possible sunlight exposure and the plants continued to extend and retract leaves on a 24-hour cycle. Conclusion: Mimosa plant must be sensing the moon. (incorrect) Conclusion: Mimosa plant must be sensing the moon. (incorrect) Circadian Rhythms closet

18. More than 100 years later, Swiss botanist, Camdolle, showed that a similar plant has a 22-hour cycle when placed in no-light conditions. More than 100 years later, Swiss botanist, Camdolle, showed that a similar plant has a 22-hour cycle when placed in no-light conditions. Conclusion: The plant must have an internal clock. (correct) Conclusion: The plant must have an internal clock. (correct) Organisms with internal clocks entrain (set) those clocks to the length of a day using external cues. Organisms with internal clocks entrain (set) those clocks to the length of a day using external cues. Light sensory information is the most influential cue Light sensory information is the most influential cue Humans fall back on their internal clock in the absence of all external daily cues (called a free-running state). Humans fall back on their internal clock in the absence of all external daily cues (called a free-running state). While some humans have internal clocks that are 24 hours, some have clocks that are less than 24 hours and some have clocks that are more than 24 hours. While some humans have internal clocks that are 24 hours, some have clocks that are less than 24 hours and some have clocks that are more than 24 hours. Evidence of an Internal Clock

19. It is hypothesized that individuals with clocks less than 24 hours are “morning people”. It is hypothesized that individuals with clocks less than 24 hours are “morning people”. Instead of having about 16 hours of awake time and 8 hours of asleep time, morning people are ready for bed sooner and sleep shorter than “24-hour people”. Instead of having about 16 hours of awake time and 8 hours of asleep time, morning people are ready for bed sooner and sleep shorter than “24-hour people”. It is hypothesized that individuals with clocks more than 24 hours are “night people”. It is hypothesized that individuals with clocks more than 24 hours are “night people”. Instead of having about 16 hours of awake time and 8 hours of asleep time, night people are ready for bed later and would sleep longer than “24-hour people”. Instead of having about 16 hours of awake time and 8 hours of asleep time, night people are ready for bed later and would sleep longer than “24-hour people”. Night vs. Morning People

20. In mammals, destruction of the suprachiasmic nucleus (SCN) in the hypothalamus abolishes circadian rhythms. In mammals, destruction of the suprachiasmic nucleus (SCN) in the hypothalamus abolishes circadian rhythms. Fairly small – 0.3 mm 2 Fairly small – 0.3 mm 2 Lies atop the optic chiasm, receiving direct light sensory input Lies atop the optic chiasm, receiving direct light sensory input Location of the Internal Clock Hypothalamus SCN Optic chiasm Pituitary

21. Circadian studies on Golden hamsters showed they normally have a 24-hour internal clock. Circadian studies on Golden hamsters showed they normally have a 24-hour internal clock. One male hamster showing a 22-hour internal clock was bred with 24-hour females. One male hamster showing a 22-hour internal clock was bred with 24-hour females. The pups fell into two groups: 24-hour and 22-hour clocks The pups fell into two groups: 24-hour and 22-hour clocks Further breeding between 22-hour hamsters resulted in some of the offspring having 20-hour clocks. Further breeding between 22-hour hamsters resulted in some of the offspring having 20-hour clocks. Gene identified and called the tau gene Gene identified and called the tau gene If a SCN of a 22-hour hamster is transplanted into the SCN of a 24-hour hamster, the hamster becomes a 22- hour hamster. If a SCN of a 22-hour hamster is transplanted into the SCN of a 24-hour hamster, the hamster becomes a 22- hour hamster. More Evidence for the SCN

22. Latest evidence suggests that the internal clock is controlled by neurons in the SCN that change their output on a cycle that is close to 24 hours. Latest evidence suggests that the internal clock is controlled by neurons in the SCN that change their output on a cycle that is close to 24 hours. Hypothesis: Hypothesis: These neurons have a gene that codes for mRNA that codes for a protein. These neurons have a gene that codes for mRNA that codes for a protein. The protein then changes the output of the neuron and inhibits further synthesis of the mRNA that created it. The protein then changes the output of the neuron and inhibits further synthesis of the mRNA that created it. This cycle of expression/inhibition takes about 24 hours. This cycle of expression/inhibition takes about 24 hours. Mechanism of the Internal Clock

23. From retina SCN neuron DNA mRNA protein output -