Localisation of Function (LOF) is a theory proposing that specific emotions, thoughts, and behaviours are linked to distinct brain regions. This concept contrasts with the holistic view of the brain, which suggests that brain functions arise from the integrated operation of the entire organ. Until the 1930s, the holistic theory dominated neuroscience, but researchers like Bard, Elwood, and others began mapping brain regions using evoked electrical potentials. By the 1970s and 1980s, evidence emerged supporting the existence of multiple maps within sensory modalities, supporting the LOF. For instance, the visual cortex is now recognised to comprise five distinct areas, including the primary visual cortex (V1), which specialises in processing static and moving objects and pattern recognition. Critics argue, however, that cognitive skills such as learning involve the entire brain rather than being confined to specific areas.
The brain consists of two hemispheres linked by the corpus callosum. Each hemisphere is thought to handle different functions: the left is responsible for rational thinking, language processing, and fine motor skills, while the right hemisphere governs holistic thinking, creativity, and cognitive functions like face recognition. Both hemispheres collaborate to facilitate intuitive and conceptual thinking, though the right hemisphere typically dominates tasks involving visual interpretation. Evidence of hemispheric functions primarily comes from MRI studies of individuals with hemisphere damage. For instance, left hemisphere damage can lead to difficulties in processing spoken and written language as well as sensory disruptions, while right hemisphere damage is associated with impulsivity and problems in reasoning and memory. Most information processing occurs in the cerebral cortex, which has four lobes: occipital, frontal, parietal, and temporal. Research supports that specific functions originate in these regions, as suggested by Lashley's equipotentiality theory, which states that basic motor and sensory functions are localized, while higher cognitive functions are not.
Neuropsychologists have identified various localized functions. In the occipital lobe, visual processing occurs, divided into five areas (V1-V5). Visual data from the thalamus first reaches the primary visual cortex (V1), where it is processed and analyzed further by other brain regions. Damage to the occipital lobe can cause visual deficits such as hallucinations and colour agnosia. For example, Zeki et al. (1991) used PET scans to identify areas within the visual cortex linked to colour perception and motion. They found that the V4 region is crucial for colour perception, evidenced by a patient with achromatopsia after two cerebral infarctions. The middle temporal visual area (V5) is involved in motion perception. Researchers examining V5 used PET and MRI techniques to show that it is essential for perceiving visual motion, supported by case studies of patients with V5 damage who experienced motion blindness (akinetopsia).
The frontal lobe is the largest of the brain's lobes and plays an important role in controlling voluntary movements and higher cognitive functions in humans, such as emotional expression and regulation, memory, attention, speech and language, decision-making, and problem-solving. One of the most prominent areas in the brain is Broca's area, located in the left posterior part of the frontal lobe. This region has long been linked to speech production, language comprehension, and the motor functions associated with speech. Neuroimaging studies indicate that Broca's area is activated during both speech production and hand movements, as well as during higher-level linguistic processing, such as understanding the reasoning behind conversations. Damage to Broca's area leads to aphasia, characterized by difficulties in speech production. In 1861, Paul Broca published the case of a patient known as "Tan," who had a lesion in the left inferior frontal gyrus, resulting in an inability to speak beyond the syllable "tan." A 2007 study by Dronkers et al. assessed Tan's brain and found that the damage extended beyond Broca's area, suggesting that this region is not the sole area involved in speech production. Additionally, neurological deficits in individuals with Broca's aphasia may affect surrounding structures.
In conclusion, the theory of Localisation of Function (LOF) provides valuable insights into the relationship between specific brain regions and their associated emotions, thoughts, and behaviours. This theory, while contrasting with the holistic view, underscores the importance of understanding how distinct areas of the brain contribute to various cognitive and motor functions. The evidence from neuroimaging studies and case analyses enhances our comprehension of the brain's complexity. As research continues to evolve, it is essential to acknowledge the interplay between localised and integrated brain functions, recognising that while certain areas may be responsible for specific tasks, the brain operates as a cohesive unit. The ongoing exploration of brain functions will not only deepen our understanding of human cognition and behaviour but also inform therapeutic approaches for individuals with neurological impairments.
References
Jawabri, K. H., & Sharma, S. (2019). Physiology, cerebral cortex functions. https://europepmc.org/article/nbk/nbk538496
Tootell, R. B., Hadjikhani, N. K., Vanduffel, W., Liu, A. K., Mendola, J. D., Sereno, M. I., & Dale, A. M. (1998). Functional analysis of primary visual cortex (V1) in humans. Proceedings of the National Academy of Sciences, 95(3), 811-817. https://www.pnas.org/doi/abs/10.1073/pnas.95.3.811
Duncan, J., & Owen, A. M. (2000). Common regions of the human frontal lobe recruited by diverse cognitive demands. Trends in neurosciences, 23(10), 475-483. https://www.cell.com/trends/neurosciences/abstract/S0166-2236(00)01633-7
Rorden, C., & Karnath, H. O. (2004). Using human brain lesions to infer function: a relic from a past era in the fMRI age?. Nature Reviews Neuroscience, 5(10), 812-819. https://www.nature.com/articles/nrn1521
Diamond, N. B., & Levine, B. (2018). The prefrontal cortex and human memory. https://osf.io/u9hgx_v1/download
Zhang, B., He, S., & Weng, X. (2018). Localization and functional characterization of an occipital visual word form sensitive area. Scientific reports, 8(1), 6723. https://www.nature.com/articles/s41598-018-25029-z
Rehman, A., & Al Khalili, Y. (2019). Neuroanatomy, Occipital Lobe. https://europepmc.org/article/nbk/nbk544320