Neuroscience and personhood

Naturalizing Personhood
Defining “Person”
The earliest explicit definition of personhood came from the sixth-century
philosopher Boethius, who equated a person with “an individual substance of a
rational nature”
For Locke, there were three essential characteristics of personhood: rationality, selfawareness, and the linkage of this self-awareness by memory across time and
For Kant: ability to distinguish between persons (rational beings) and things and
treat them accordingly. Rational beings exist as ends in and of themselves and means
to ends, as are things.
Defining “Person”
More recent:
Daniel Dennett: the ability to understand others
as having intentional mental states, which requires
language. Language confers a “special
consciousness.” Dennett concedes that all
definitions of personhood suffer from
arbitrariness. That is – were are imposing
dichotomous distinctions on continuous or
multifaceted traits (language, memory, selfawareness, morality, etc.).
Joseph Fletcher: 15 criteria for personhood (usual
suspects – memory, language, self-awareness,
etc), including a specific IQ scores, (at least above
20). Arbitrariness: why is a 21 a person, while a 20
is not?
Authors’ conclusion: satisfactory defining criterion
or criteria for personhood – illusive.
“We are left setting criteria that feel, in Dennett’s
words, arbitrary. In effect, personhood is a concept
that everyone feels they understand but no one
can satisfactorily define.” (p. 39).
Neuroscience of personhood
• Neuroscience will allow us to
translate the psychological
criteria for personhood
(language, self-awareness,
memory, etc) into neurological
criteria. But this will not
eliminate problem of defining
personhood. It will only give it a
different vocabulary.
• Nearly all criteria for
personhood refer to neocortical
brain function. Is a person
someone with a functioning
• Problem: brain development is
gradual not punctuate. When
exactly does “brain life” begin?
Brain-created reality
• We live in the world our brains create. If the brain cannot
process it, we do not experience it. We can only experience
the categories the brain represents. This is true both for
physical categories (red vs. blue; cold vs. hot, sweet vs.
salty, etc) as well as social categories (persons vs. non
The brain’s “person” system
• Early evidence suggesting its
existence: Prosopagnosia -- a
specific deficit in face recognition
due to damage in the temporal
lobe, equally complex pattern
recognition can be preserved, only
faces affected. Also, inverse
disorder has also been
documented – globally pattern
recognition disorder with
preserved face recognition.
Indicating dedicated face
recognition system in brain
• Location of face recognition area:
fusiform gyrus of temporal lobe
• Fusiform face area only one part
of a larger “person” system
The brain’s “person” system
• Human body recognition area(s):
fusiform gyrus separate from face
area and temperoparietal juncture
• Part of TPJ also responds to body
movements with different parts
responding to goal-directed
movements and another when
thinking about another’s mental
state. “She’s biting her lip because
she wants him to think that she’s
• Medial Prefrontal cortex: also
involved in TOM, thinking about
other’s mental states. For example,
if people think they are playing
“rock-paper-scissors” with another
person MPC active. If they think
they are playing with computer,
MPC less active.
The brain’s “person” system
• Summary of person system
• FFA: face recognition
• FFG & TPJ: human body recognition, goal directed
action recognition, thoughts behind actions
The brain’s “person” system
• System shows evidence of
being both autonomous and
• Autonomous: system will
engage automatically with
minimal evidence and even
when we know consciously
and rationally that no person
is present.
• For example: children and
adults will describe geometric
forms “chasing” each other as
goal-directed agents
compelled by emotions.
The brain’s “person” system
• Innateness: present at birth with little or no learning required.
• For example: infants as young as 30 mins after birth will track face-like
pattern more than equally complex other patterns. Damage as early as 1
day after birth to FFA, will lead to lifelong deficit in face recognition. Other
pattern recognition areas do not take over function.
• Habituation studies: By 5 months, infant expect human, but not
mechanical, movements to be rational. So if a human reaches around a
barrier to get an object and the barrier is subsequently removed, infants
are not surprised if the human reaches directly for the object. They are
surprised if a mechanical arm reaches directly for object.
• Autism studies show less activity in person system.
What does this tell us about personhood?
• Because the person system is autonomous (separate from other brain
systems) it encourages the illusion that personhood exists as a distinct
entity out in the world. When it kicks in, there is a person out there, when
it does not there is no person out there.
• But since it is designed to react to minimal stimulation it frequently over
identifies persons. It says “person” when our rational brain knows there is
no person.
• Over attributing personhood is adaptive, we all start life as non-persons!!
• Personhood defined by a specific criterion (or criteria) may be futile.
• Note: other philosophical approaches define personhood by relationships
with others.

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