18) Behavior exists on a continuum between controlled and automatic processing (Schneider & Shiffrin – 1977) During the 1970s those studying the cognitive computations underlying visual search were at an impasse. One group of researchers claimed that visual search was a flat search function (i.e., adding more distracters doesn't increase search time), while another group …
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17) Reverbatory activity in lateral prefrontal cortex maintains memories and attention over short periods (Fuster – 1971, Jacobsen – 1936, Goldman-Rakic – 2000) Patient H.M., with his lack of long term memory but largely intact working (short-term) memory, illustrated a dissociation between these two forms of memory. While long-term memory seemed to rely on hippocampus …
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16) Critical periods of cortical development via competition (Hubel & Wiesel – 1970) Hubel & Wiesel showed that the ocular dominance columns they had discovered in cortex (see previous post) are organized during a critical period of development. Keeping one eye of an animal shut during the first few months of life made that animal …
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15) Consciousness depends on cortical communication; the cortical hemispheres are functionally specialized (Sperry & Gazzaniga – 1969) It is quite difficult to localize the epileptic origin in some seizure patients. Rather than removing the gray matter of origin, neurosurgeons sometimes remove white matter to restrict the seizure to one part of the brain. One particularly …
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14) Neocortex is composed of columnar functional units (Mountcastle – 1957, Hubel & Wiesel – 1962) Mountcastle found that nearby neurons in monkey somatosensory cortex tend to activate for similar sensory experiences. For example, a neuron might respond best to a vibration of the right index finger tip, while a neuron slightly deeper in might …
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13) Larger cortical space is correlated with greater representational resolution; memories are stored in cortex (Penfield – 1957) Prior to performing surgery, Wilder Penfield electrically stimulated epileptic patients' brains while they were awake. He found the motor and somatosensory strips along the central sulcus, just as was found in dogs by Fitsch & Hitzig (see …
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12) Hippocampus is necessary for episodic memory formation (Milner – 1953) Patient H.M. had terrible epilepsy originating in the medial temporal lobes. His neurosurgeon decided to take out the source of the epilepsy: the hippocampus. Surprisingly, after the operation H.M. could no longer form new long-term memories. He could remember things for short time periods …
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11) Action potentials, the electrical events underlying brain communication, are governed by ion concentrations and voltage differences mediated by ion channels (Hodgkin & Huxley – 1952) Hodgkin & Huxley developed the voltage clamp, which allows ion concentrations in a neuron to be measured with the voltage constant. Using this device, they demonstrated changes in ion …
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10) The Hebbian learning rule: 'Neurons that fire together wire together' [plus corollaries] (Hebb – 1949) D. O. Hebb's most famous idea, that neurons with correlated activity increase their synaptic connection strength, was based on the more general concept of association of correlated ideas by philosopher David Hume (1739) and others. Hebb expanded on this …
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9) Convergence and divergence between layers of neural units can perform abstract computations (Pitts & McCulloch – 1947) Pitts & McCulloch created the first artificial neurons and artificial neural network. In 1943 they showed that computational processing could be performed by a series of convergent and divergent connections among neuron-like units. In 1947 they demonstrated …
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8) Reward-based reinforcement learning can explain much of behavior (Skinner – 1938, Thorndike – 1911, Pavlov – 1905) B. F. Skinner showed that reward governs much of human and animal behavior. He discovered operant conditioning, a method for manipulating behavior so powerful he could teach a pigeon to bowl (or a dog to jump on …
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7) Brain signals are chemical (Dale – 1914, Loewi – 1921) Loewi found that electrically stimulating a heart causes it to release a chemical substance which changes the beating of a different heart when exposed to that chemical substance. Dale had already discovered neurotransmitters, one of which (acetylcholine) was the chemical responsible for the change …
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6) Neural networks consist of excitatory and inhibitory neurons connected by synapses (Sherrington – 1906) Based on his observations in the spinal cord, Sherrington theorized that the brain consists of complex networks of excitatory and inhibitory cells he was the first to term 'neurons', with connection points he was the first to term 'synapses'. His …
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5) Neurons are fundamental units of brain computation (Ramon y Cajal – 1889) Golgi, a prominent 19th century biologist, argued that the brain is one unified reticulum (or web) of neural tissue, much like the circulatory system. However, Ramon y Cajal came to a very different conclusion using Golgi’s very own silver chromate staining technique. …
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4) Functions can be localized in the brain (Bouillaud – 1825, Broca – 1861, Fritsch & Hitzig – 1870) Bouillaud and Broca discovered patients with frontal cortex lesions who had speech problems. Fritsch & Hitzig discovered primary motor cortex; a specialized chunk of cortex specifically for motor control. Broca believed that all brain functions would …
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