Lecture notes Brain And Behaviour I

Brain and behaviour session 4: the relationship between
brain size and behaviour

 Savant syndrome – brain damage brought about through a traumatic birth – lack the
ability to look after themselves but can develop heightened abilities in different
areas (music, art, languages)
 Does overall brain size predict behavioural differences across species?
 Neuroethology – a comparative approach looking at the brain across different
species and how these are suited to their environment – proposed by Darwin ‘theory
of evolution’ – anatomical changes in a species which help to aid survival
 Does absolute brain size correlate with cognitive ability? Macaque brain is smaller
than a cow brain – studied as display human like social interaction however cow
brain is larger but less rich in higher cognitive functional ability
 Allometry – the importance of brain size relative to body size – body weight is an
important factor in relation to brain size – increased brain size results in increased
brain size – some animals however will have either a larger or smaller brain size than
that predicted due to body size (residual brain size – larger than predicted)
 Residual brain size is related to more complex behaviour – howler monkey and
squirrel monkey have same body size yet different brain sizes – squirrel monkeys
have a larger residual brain size which results in more a more complex pattern of
behaviour such as eating patterns may suggest why brain size is larger – more
complex behaviour can result in a greater residual brain size which reflects why
different
 Evolution of the human brain and cognition – over the course of human evolution
from homo habilis to homo sapien the human body has increased in weight/size
(50%) alongside this the residual brain size has also increased (200%) as a result of
increase the cognitive ability has also developed to become more complex
 Genes may underlie evolutionary changes in brain size – microencephaly gene which
causes brain size to be much smaller than residual brain size (found across speices) –
in evolution the impact of the microencephaly gene has become greater and more
destructive
 Does the size of brain regions predict behavioural differences across species?
 The localization of function – where certain behaviours/functions are localised
 Evolutionary specializations of brain and behaviour – bats use of echolocation in
order to find food
 The principle of proper mass – dolphins live in environments where vision is
impaired so as a result hearing is advance, ibex however need vision in order to
survive – within the mid-brain there is the superior colliculus (important for vision)
inferior colliculus (important for hearing) – dolphins have a larger IC whereas an ibex
have a larger SC this relates to the principle of proper mass whereby regions that are
more needed within a species are considerably larger than another
 Overrepresentation of critical body parts in sensory and motor maps – in humans
sensory regions are disproportionately larger than regions related to hands or face –
control of face and hand are again disproportionately larger than the main body
mass – in rats whiskers are over represented in the cortex of the brain a barrel –
each whisker is relative