section_path: Relation to matter/Brain areas and processes
section_name: Brain areas and processes
paragraph_text: Brain areas and processes
  
  Another approach to the relation between mind and matter uses empirical observation to study how the brain works and which brain areas and processes are associated with specific mental phenomena. The brain is the central organ of the nervous system and is present in all vertebrates and the majority of invertebrates. The human brain is of particular complexity and consists of 86 billion neurons, which communicate with one another via synapses. They form a complex neural network and cognitive processes emerge from their electrical and chemical interactions. The human brain is divided into regions that are associated with different functions. The main regions are the hindbrain, midbrain, and forebrain. The hindbrain and the midbrain are responsible for many biological functions associated with basic survival while higher mental functions, ranging from thoughts to motivation, are primarily localized in the forebrain.
  
  The primary operation of many of the main mental phenomena is located in specific areas of the forebrain. The prefrontal cortex is responsible for executive functions, such as planning, decision-making, problem-solving, and working memory. The role of the sensory cortex is to process and interpret sensory information, with different subareas dedicated to different senses, like the visual and the auditory areas. A central function of the hippocampus is the formation and retrieval of long-term memories. It belongs to the limbic system, which plays a key role in the regulation of emotions through the amygdala. The motor cortex is responsible for planning, executing, and controlling voluntary movements. Broca's area is a separate region dedicated to speech production. The activity of the different areas is additionally influenced by neurotransmitters, which are signaling molecules that enhance or inhibit different types of neural communication. For example, dopamine influences motivation and pleasure while serotonin affects mood and appetite.
  
  The close interrelation of brain processes and the mind is seen by the effect that physical changes of the brain have on the mind. For instance, the consumption of psychoactive drugs, like caffeine, antidepressants, alcohol, and psychedelics, temporarily affects brain chemistry with diverse effects on the mind, ranging from increased attention to mood changes, impaired cognitive functions, and hallucinations. Long-term changes to the brain in the form of neurodegenerative diseases and brain injuries can lead to permanent alterations in mental functions. Alzheimer's disease in its first stage deteriorates the hippocampus, reducing the ability to form new memories and recall existing ones. An often-cited case of the effects of brain injury is Phineas Gage, whose prefrontal cortex was severely damaged during a work accident when an iron rod pierced through his skull and brain. Gage survived the accident but his personality and social attitude changed significantly as he became more impulsive, irritable, and anti-social while showing little regard for social conventions and an impaired ability to plan and make rational decisions. Not all these changes were permanent and Gage managed to recover and adapt in some areas.