Localisation of function in the brain refers to the idea that specific areas of the brain are
responsible for particular physical and psychological functions. This concept contrasts with
the holistic theory, which posits that the entire brain is involved in all processes. The
localisation theory has been supported by various studies and evidence from
neuropsychology, neuroimaging, and clinical observations.
One of the seminal contributions to the theory of localisation came from the work of Paul
Broca in the 1860s. Broca studied patients with damage to a region of the frontal lobe in the
left hemisphere, later known as Broca’s area. These patients exhibited significant
impairments in speech production, though their understanding of language remained intact.
This finding provided strong evidence that Broca’s area is crucial for language production.
Conversely, Carl Wernicke identified another area in the left hemisphere, now known as
Wernicke’s area, which is essential for language comprehension. Patients with damage to
this region could produce speech but it was often nonsensical, and they struggled to
understand language, indicating a localisation of language comprehension.
Further support for localisation of function comes from the case of Phineas Gage, a railroad
worker who survived an accident in which a metal rod penetrated his skull and damaged his
frontal lobes. Following the accident, Gage exhibited profound changes in personality and
behaviour, suggesting that the frontal lobes are involved in regulating emotions and social
behaviour. This case highlights the localisation of more complex psychological functions
beyond sensory and motor skills.
Neuroimaging techniques, such as fMRI and PET scans, have provided additional support
for the localisation of function. These techniques allow researchers to observe brain activity
in real-time and have consistently shown that specific tasks activate particular brain regions.
For instance, fMRI studies have shown that the occipital lobes are primarily involved in visual
processing, while the temporal lobes are crucial for auditory processing.
Despite substantial evidence supporting localisation, some research suggests a more
nuanced view. Lashley’s research on rats, for example, involved lesioning different areas of
the cortex and observing the effects on maze learning. Lashley found that the extent of
cortical damage, rather than its location, was more predictive of impairment, leading him to
propose the principle of equipotentiality. This principle suggests that while certain areas may
be specialised, the brain has a remarkable ability to adapt and compensate for damaged
regions, indicating some degree of functional redundancy and plasticity.
The notion of brain plasticity further complicates the localisation theory. Neuroplasticity refers
to the brain’s ability to reorganise itself by forming new neural connections throughout life.
For instance, in cases of brain injury, other parts of the brain can sometimes take over the
functions of the damaged areas, as observed in stroke patients who recover lost functions
through rehabilitation and therapy.
Moreover, research into neural networks highlights that while localisation of specific
functions exists, these functions often rely on interconnected networks that span multiple
brain regions. For example, the Default Mode Network (DMN), involved in self-referential
and introspective thought processes, includes parts of the frontal, parietal, and temporal
lobes.
