The human brain, a complex organ, is the seat of our thoughts, emotions, and perceptions. Understanding what thoughts are made of involves exploring the intricate biological and chemical processes within it. This article examines the scientific understanding of how thoughts arise, from the brain’s microscopic components to the broader questions about subjective experience.
The Brain’s Microscopic Building Blocks
Thoughts originate from the activity of specialized cells called neurons, the fundamental units of the nervous system. The human brain contains over 100 billion neurons. Each neuron has three main parts: dendrites, a cell body (soma), and an axon.
Dendrites are tree-like branches that receive incoming electrical and chemical signals from other neurons. The cell body contains the nucleus and other organelles, maintaining the neuron’s function. The axon is a long, tube-like structure that transmits electrical impulses away from the cell body to other neurons.
Neurons communicate at junctions called synapses, tiny gaps between the axon terminal of one neuron and the dendrite of another. When an electrical signal, an action potential, reaches the end of an axon, it triggers the release of chemical messengers called neurotransmitters into the synaptic cleft. These neurotransmitters then bind to receptors on the receiving neuron, which can either excite or inhibit that neuron from generating its own action potential.
How Brain Activity Creates Thoughts
Individual neuron activity scales up to form complex thoughts through the coordinated actions of vast numbers of neurons organized into intricate neural networks and circuits. Information processing within the brain involves the continuous firing of neurons, where the sum of electrical pulses from multiple inputs determines if a neuron will generate an action potential and transmit a signal. This dynamic interplay forms the basis of all mental processes.
Thoughts arise from distributed activity across different brain regions. The cerebral cortex, the brain’s outermost layer, is involved in higher-level processes like language, memory, reasoning, and decision-making. It is divided into four main lobes: frontal, parietal, temporal, and occipital.
Each lobe processes different types of information. The frontal lobe is linked to planning, problem-solving, and abstract thought, while the occipital lobe is dedicated to visual processing. The coordinated activity within and between these specialized regions, along with deeper brain structures, allows for the integration of sensory input, memory formation, and the generation of conscious thoughts. This system transforms raw sensory data into meaningful perceptions and complex ideas.
The Subjective Experience of Thinking
Even with a detailed understanding of neuronal activity and brain networks, the transition from physical brain processes to the subjective, conscious experience of thinking remains an active area of scientific inquiry. This is often referred to as the “hard problem” of consciousness, asking why and how physical brain states give rise to our inner, qualitative experiences. While neuroscience can identify neural correlates—specific patterns of brain activity associated with conscious experiences—it does not fully explain why these physical events produce subjective awareness.
Various theories attempt to bridge this gap between brain activity and conscious experience. The Global Neuronal Workspace Theory suggests that consciousness emerges when information becomes widely accessible across multiple brain systems through a network of neurons. Another perspective, the Integrated Information Theory, proposes that consciousness is a fundamental property of any system with a certain degree of “integrated information,” meaning its capacity for conscious experience is tied to how much information it generates beyond its individual parts.
Other ideas explore the possibility that quantum phenomena within the brain’s microtubules, tiny protein structures within neurons, might play a role in consciousness. These hypotheses are still unvalidated and debated within the scientific community. While we can map brain activity and observe correlations with conscious states using technologies like fMRI, fully explaining the “what it is like” aspect of subjective experience continues to be a profound challenge.