Lecture 10 - Interfering With Brain Function Flashcards
Electric and magnetic brain stimulation - Transcranial magnetic stimulation (TMS) & transcranial direct current stimulation (tDCS)
Brain stimulation: noninvasive technique using a magnetic coil to induce a voltage or electrodes to induce current into brain tissue
Inhibition and facilitation brain function
Valuable in both research and therapeutically
Interfere - analyses of causality:
Most neuroimaging methods provide correlational evidence
In fMRI and EEG or proving true causality can br challenging
TMS/TDCS adds “neural noise” to a neuronal system, temporarily disrupting or enhancing its function
Brain stimulation can be used to investigate the causal function of a target brain area
If brain stimulation of a specific area either increases or decreases performance, we can try assume that area has a causal role in behaviour
TMS works using a TMS coil and electric current to create a magnetic field which induces current in the brain
We manipulated brain function, now what?
Repetitive TMS can create ‘virtual lesions’
Brain regions can become temporarily impaired or disconnected,allowing us to study their casual involvement in certain brain functions
Control condition for TMS experiments:
- usually the same person does the same task at a different time
- often called ‘sham’ condition where a fake pulse is emitted or a different brain region is affected (that ideally is not involved in the studied process)
In order to test the causal contributions of a brain region to behaviour, we need to combine the TMS technique with carefully designed behavioural experiments
IF the brain region is causally involved in certain functions, TMS will cause difference in performance (errors) and speed (reaction times) compared to a control condition
Benefits of TMS
Brain research:
Precise localisation of brain regions (at least close to skull)
- much better localisation than experiments with brain lesion patients
- can be used in combination with EEG and fMRI
Temporary brain impairment without long term consequences
- saving a lot of lives of test animals
- we can study the effect of brain function disruption in the same person
Medical research and application:
Many therapeutic benefits of TMS for many medical conditions including:
- depression
- addiction
- stroke rehabilitation
- Parkinson’s disease
- chronic brain
Transcranial direct stimulation (tDCS)
Made up of:
Anode - the anode, or positively charged electrode, can stimulate neuronal activity in different parts of the brain
Cathode - the cathode, or negatively charged electrode, can inhibit brain-cell activity
Wires - two electrodes can provide different types of stimulation, depending on where they were placed. Together, they make a complete circuit
Device - a battery-powered device delivers a constant electrical current of up to 2mA (milliamperes). Researchers have demonstrated that it’s safe to apply thus much current for up to 30 minutes a day. DIY brain stimulators frequently use a 9-volt battery as a power source
Some studies show that stimulating the brain with electricity can immediately boost memory, focus, energy and vigilance. Researchers say that it also shows promise as a means of treating drug-resistant mental illness like depression, as well as conditions like epilepsy and chronic pain
Non-invasive, painless brain stimulation treatment that uses direct electrical currents to stimulate specific parts of the brain
A constant, low intensity current is passed through two electrodes placed over the head which modulates neuronal activity
Two types of stimulation with tDCS: a nodal and cathedral stimulation
- anodal stimulation typically acts to excite neuronal activity
- cathedral stimulation typically inhibits neuronal activity
Advantages of tDCS
Cheap, non-invasive, painless, safe
Easy to administer and the equipment is portable
Minimal side effects with proper application (most common side effect is a slight itching or tingling on the scalp)
Studies suggest tDCS may be a valuable tool for the treatment of neuropsychiatric conditions such as depression, anxiety, Parkinson’s disease, chronic pain, traumatic brain injury and stroke, and for relieving symptoms related to: language and movement disorders and impaired cognition
Research has also demonstrated cognitive improvement
BUT
Too easy, too hip, too promising -> prone for abuse
(Long-term) cognitive consequences not clear
Drugs (substance/chemical brain stimulation)
Intoxication is the 4th most important instinct after hunger, thirst and sex
Different ways drugs may be used:
- to improve athletic performance
- to improve cognitive performance
- for relaxation
- recreationally
Some drugs that aren’t necessarily thought to be drugs include:
- alcoholic beverages
- pain killers
- caffeine
- nicotine
- prescription medication for mental health
- synthetic hormones (e.g. birth control, testosterone)
How do painkillers work?
They do 2 things:
1. Depressing the nervous system, making it harder for pain signals to reach the brain
2. Attaching to opiate receptors to block pain signals coming from the body
NSAIDs like aspirin and ibuprofen block an enzyme used by injured cells to make prostaglandins (the body’s pain messengers)
When cells don’t release prostaglandins, the brain won’t get the pain message as quickly or clearly
No known cognitive effects but may protect against neurodegenerative diseases
Paracetamol (acetaminophen) is not an NSAID and won’t affect the injured cell
It treats pain by blocking the enzyme receptors in the brain, but nit much in the rest of the body, meaning the pain is there but your mind won’t receive the message
Cognition: can improve spatial memory and decision making, impaired error detection
Beta-blockers against anxiety
When you are anxious, your brain makes adrenaline and noradrenaline (stress hormones)
These make your heart rate faster and make you sweat or shake
Beta-blockers like propranolol block the effects of these hormones, which reduces the physical signs of anxiety (e.g. decrease heart rate)
But the downside is that propanol can also suppress positive stress/arousal (not all stress is bad), which can result in loss of libido, erectile dysfunction and depression
Cognitive effects: can impact perception and motor function, may improve complex task performance
Medical and illicit stimulants
Increase psychomotor and sympathetic nervous system activity, improve alter ness and mood by increasing dopamine and adrenaline
Rapid uptake e.g. by inhaling also leads to rapid short lived reward, linked to addiction
They have medical and recreational application
Increase heart rate, construct blood vessels, dilate pupils, inhibit salivation & digestion, ease anal congestion, appetite suppression, hypothermia
Cognitive effects: enhance cognitive control, memory and attention
Amphetamines such as:
- Ritalin/concerta/ADHD drugs
- MDMA/ecstasy
- Crystal meth
Amphetamines improve sustained attention, reduce over activity and impulsiveness
Cocaine:
Local anaesthetic and restricts blood vessels (useful to surgeries as anaesthetic and to stop bleeding)
Hallucinogens/psychedelic drugs
Drugs (e.g. LSD, ketamine, mescaline, psilocybin, DMT, ecstasy, magic mushrooms, morning glory seeds, peyote) that induce reality-altering experiences (hallucinations, sensory distortions or delusions)
True hallucinations: perception of images or sounds that are not real
Pseudo-hallucinations: altered perception of things that are real, synaesthesia
Approx 9% of adults use hallucinogenic substances
Regular users often have a mood disorder, in addition to substance, eating or personality disorders
Several hallucinogens are currently in experimental trials for treatment of depression
Most hallucinogenics target serotonin receptors (the the visual & sensory cortices & media-frontal cortex)
Serotonin modulates mood, cognition, reward, learning, memory and numerous physiological processes (e.g. vomiting) and links to depression and ASD, but not yet fully understood
Very low addictive potential
Cognitive effects: perceptual distortions, cognitive restructuring, mood changes, changes in meaning of perceptions and dissolution of bodily boundaries
