senses

There’s a lot of different senses

The platypus detects pray using electrosensing to detect the activity of neurons in animals around it

There’s a lot of different senses

Uses electrolocation to hunt prey

There’s a lot of different senses

The reality you experience depends on which senses you have

Uses electrolocation to hunt prey

Why do different animals have different senses?

We have the senses that our ancestors needed to survive

How the brain learns about the world

How the brain learns about the world

light

Neural activity

Magnetic field

Air vibrations

Molecules in food

Sensing before neurons

Escherichia Coli

Sensing before neurons

An example: hearing

and balance

An example: taste

The brain assigns a “meaning” to sensory information based which neurons get activated, not what they get activated by

How the brain learns about the world

light

Neural activity

Magnetic field

Air vibrations

Molecules in food

The brain then needs to make sense of the neural activity it receives to reconstruct the physical phenomena

Sensory cortical areas

Blind vision

...or an example of how complicated things can be

senses AMA

daily responses

mini BrainCamp 2020-04-28

neuroendocrinology

many of the feelings we experience on a daily basis are mediated by an interaction between the nervous and endocrine systems

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AFFERENT (input)

EFFERENT (output)

somatic senses

special senses

visceral senses

somatomotor

autonomic

neuroendocrinology

autonomic nervous system consists of sympathetic & parasympathetic

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acetylcholine + noradrenaline

​

acetylcholine

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fight or flight

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rest and digest

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love

stress

hunger

neuroendocrinology

stress

first response to stress: fight or flight (seconds)

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mediated by the sympathetic nervous system

sweating

goosebumps

abdominal sensations

heightened awareness

higher blood pressure

rapid pulse rate

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diverts blood flow to vital organs: muscles & brain

central nervous system

sympathetic chain

adrenal glands

acetylcholine

noradrenaline*

*except sweat glands

adrenaline

adrenal glands

adrenal medulla (adrenaline)

stress

second response to stress: the HPA axis (~2 min)

hypothalamus

pituitary gland (anterior)

adrenal glands

anterior pituitary

hypothalamus

adrenal glands

CRH

ACTH

cortisol

CRH - corticotropin releasing hormone

ACTH - adrenocorticotropic hormone

adrenal cortex (cortisol)

cortisol raises blood sugar & fatty acids, helps adrenaline raise blood pressure,

suppresses growth, digestion, healing

cortisol acts on amygdala to promote learning of fear-related information

the right amount of stress for your hippocampus

mild / short-term hippocampal suppression can help focus, prevent unnecessary learning

extreme / prolonged stress can alter hippocampal morphology and function

cortisol suppresses the hippocampus

severe depression often manifests cortisol overproduction & hippocampal shrinkage

elevated cortisol might also play a role in age-related memory deficits

high-affinity mineralocorticoid receptor

low-affinity glucocorticoid receptor

positive

negative

mechanism behind the dual effects

how can one hormone — cortisol — have such different effects?

stress: recap

primary response to stress is mediated by the sympathetic system

it involves noradrenaline acting on the adrenal medulla

secondary response to stress is mediated by the HPA axis

it involves secretion of cortisol from the adrenal cortex

a little bit of cortisol helps you focus

too much cortisol is linked to depression & memory deficits

hunger

food intake is regulated by meal-related & energy store signals

the only hunger hormone

secreted by stomach

secreted by fat cells

promotes satiety

nutrients determine satiety duration

hunger

the central regulator of food intake is the hypothalamus

HYPOTHALAMUS

hypothalamus

sight & smell of food

eat

nutrients & hormones

hunger

an important hypothalamic site is the arcuate nucleus

leptin

ghrelin

+

+

–

–

fast

eat

POMC neurons

stimulated by leptin & insulin

reduce appetite

AgRP neurons

stimulated by ghrelin

promote food intake

from Chen et al. (2015)

food discovery neurons?

hunger

an important hypothalamic site is the arcuate nucleus

neural response magnitude depends on food palatability & accessibility

from Chen et al. (2015)

the power of sugar

sugar preference in mice is mediated by the solitary nucleus in brainstem

sugar is signalled by the vagus nerve

without involving the taste system

from Tan et al. (2020)

preference is specific to natural sugar

the circuit can be co-opted to prefer other things!

food intake is regulated by meal-related & energy store signals

the only hunger hormone is ghrelin

its actions are opposed by many hormones, including leptin

the main central regulator of food intake is the hypothalamus

hypothalamic arcuate nucleus contains food-discovery neurons

sugar preference is mediated by the vagus nerve & solitary nucleus

hunger: recap

what is love?

attraction

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lust

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attachment

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motivates individuals to mate

focuses mating energy on specific mates

motivates mates to remain together long enough

to perform species-specific parental duties

baby don’t hurt me, don’t hurt me, no more

from Seshadri (2016)

what is love?

attraction

​

lust

​

attachment

​

motivates individuals to mate

focuses mating energy on specific mates

motivates mates to remain together long enough

to perform species-specific parental duties

associated with androgens & oestrogens

hypothalamus

sexual preference�(dimorphic nuclei, e.g.,

medial preoptic area

suprachiasmatic nucleus)

amygdala

arousal, alertness

what is love?

attraction

​

lust

​

attachment

​

motivates individuals to mate

focuses mating energy on specific mates

motivates mates to remain together long enough

to perform species-specific parental duties

associated with androgens & oestrogens

ventral tegmental

area

reward

nucleus accumbens

pleasure

exhilaration, intrusive thinking, courtship

associated with high dopamine, low serotonin

prefrontal cortex

planning, execution

other courtship behaviours

ornamental display of peacocks

elaborate mating ritual in fruit flies

male stickleback performs a zigzag dance

vocalisations in male frogs

what is love?

attraction

​

lust

​

attachment

​

motivates individuals to mate

focuses mating energy on specific mates

motivates mates to remain together long enough

to perform species-specific parental duties

associated with androgens & oestrogens

ventral pallidum

pairbonding

nucleus accumbens

social recognition

exhilaration, intrusive thinking, courtship

associated with high dopamine, low serotonin

associated with oxytocin & vasopressin

love in prairie voles

naturally monogamous: preference linked to higher dopamine in nucleus accumbens

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dopamine blockers can abolish preference,

dopamine activators can switch preference

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lust

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drop of male urine onto the upper lip triggers oestrogen release in females

attraction

​

attachment

​

vasopressin blockers prevent formation of preference for a single partner

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perturbation of oxytocin activity reduces side-by-side behaviours

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heartbreak

many of the attraction circuits are still active:

the brain is addicted (mesolimbic)

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ventral tegmental

area

nucleus accumbens

orbitofrontal cortex

prefrontal cortex

the brain is conflicted (OFC)

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from Fisher et al.

(2005)

the brain is in pain (operculum)

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operculum

(& anterior insula)

the final stage of grief – acceptance –

involves more activity in posterior brain regions

three types of romantic love: lust, attraction & attachment

lust is associated with oestrogens & androgens

attraction is associated with dopamine & shortage of serotonin

attachment is associated with oxytocin & vasopressin

most ‘evidence’ comes from human fMRI & questionnaires

a popular animal model in love research has been the prairie vole

love: recap

History of neuroscience

Black bile: related to earth, with cold and dry properties

Yellow bile: related to fire, with dry and warm properties.

Blood: related to air, with moist and warm qualities.

Phlegm: related to water, with moist and cold qualities.