Scientific Understanding of Consciousness
Consciousness as an Emergent Property of Thalamocortical Activity

Thalamocortical System — Informative Paraphrases

 

 

Edelman has a very informative discussion; here is an excerpt: Thalamocortical system evolved to receive signals from sensory receptor sheets and give signals to voluntary muscles. Thalamocortical system is very fast in its responses (milliseconds to seconds), although its synaptic connections undergo some changes that last a lifetime. Cerebral cortex is arranged as a set of maps, which receive inputs via the thalamus. Thalamocortical system does not contain loops so much as highly connected layered local structures with massively reentrant connections. (Edelman; Bright Air, 117)

An informative discussion of thalamocortical loops contrasting the oscillatory state of NREM sleep and the tonically active state of wakefulness/REM sleep. (Purves; Neuroscience, 679-81)

Thalamocortical system gives rise to the dynamic core, represented by a fine meshwork of cortical and thalamic areas and reentrant connections -- (diagram) (Edelman; Bright Air, 179)

Consciousness is a product of thalamocortical activity. Dialogue between the thalamus and the cortex generates subjectivity in humans and in higher vertebrates. (Llinás; I of the Vortex, 131)

Wikipedia has a “stub” article on thalamocortical loops.

Thalamocortical system  -  dense meshwork of reentrant connectivity between the thalamus and the cortex and between the cortical regions. (Edelman; Bright Air, 43)

Conscious experience is associated with the activity of populations of neurons that are widely distributed in the thalamocortical system. The distributed groups of neurons must engage in strong and rapid reentrant interactions. (Edelman; Bright Air, 62)

Thalamocortical circuits mediating these reentrant interactions originate in the major subdivisions of the thalamus: specific thalamic nuclei, reticular nucleus, intralaminar nuclei. (Edelman; Universe of Consciousness, 107)

Large-scale computer simulations show that reentry is the key neural mechanism by which integration can be achieved within the thalamocortical system. (Edelman; Universe of Consciousness, 113)

Integration and rapid functional clustering occur in the thalamocortical system, and reentry is the major mechanism for achieving integration. (Edelman; Universe of Consciousness, 124)

Thalamocortical system -- even of a fetus in utero -- is spontaneously active whether or not it receives inputs form outside. (Edelman; Universe of Consciousness, 136)

Global mapping links the thalamocortical system with the subcortical appendages

Global mapping relates an animal's movement and changing sensory input to the action of the hippocampus, basal ganglia, and cerebellum as they connect to the cerebral cortex. Thus a global mapping links the thalamocortical system with the subcortical appendages. (Edelman; Universe of Consciousness, 95)

Unconscious neural processes occurring in the sensory and motor periphery can influence the dynamic core. Ongoing unconscious assistance to our conscious life occurs whenever we speak aloud or only to ourselves, write or type, play a musical instrument, perform athletic routines, drive an auto or simply set a table. It occurs when we perform a mental calculation or merely follow a train of thought without doing or saying anything.(Edelman; Universe of Consciousness, 182)

Dynamic core -- ever-changing composition yet ongoing integration, is generated largely, although not exclusively, within the thalamocortical system. (Edelman; Universe of Consciousness, 139)

Every conscious task seems to require the activation or deactivation of many regions of the brain, typically including portions of the thalamocortical system. (Edelman; Universe of Consciousness, 140)

Dynamic core -- an integrated process that is generated largely in the thalamocortical system. (Edelman; Universe of Consciousness, 177)

Thalamocortical system gives rise to the dynamic core, represented by a fine meshwork of cortical and thalamic areas and reentrant connections -- (diagram) (Edelman; Universe of Consciousness, 179)

Neuroanatomical and neurophysiological bases for automatic routines and subroutines that interface with the core. A series of polysynaptic loops leave the thalamocortical system, run through the cortical appendages, such as the basal ganglia and cerebellum, and subsequently make their way back to the thalamocortical system. (Edelman; Universe of Consciousness, 183)

Basal ganglia are a set of huge nuclei in the depths of the forebrain that contain a vast number of neurons and that have evolved in parallel with the thalamocortical system. (Edelman; Universe of Consciousness, 184)

Activity in the thalamocortical system leads to the formation of a large functional cluster of high complexity -- the dynamic core. (Edelman; Universe of Consciousness, 185)

Active thalamocortical islands or splinters broken away from the dominant dynamic core. (Edelman; Universe of Consciousness, 190)

 

Fornical-thalamocortical path. (Edelman; Remembered Present, 130)

Matching or linking between category and value is based on two very different kinds of nervous structures and functions: (1) the limbic and brain-stem system, (2) the thalamocortical system. (Edelman; Remembered Present, 152)

Thalamocortical system; strongly linked  to exteroceptors; consists of thalamocortical reentrant system, primary and secondary sensory areas, and association areas; strongly linked to the main cortical appendages, cerebellum, hippocampus, and basal ganglia. (Edelman; Remembered Present, 152)

Thalamocortical system main functions are correlated with perceptual and conceptual categorization, memory, and learning. (Edelman; Remembered Present, 152)

Thalamocortical system is highly interconnected, reentrant, and layered local synaptic structure. Appeared as a later evolutionary development permitting increasingly sophisticated motor behavior. (Edelman; Remembered Present, 152)

Matching of the two disparate neural systems, limbic and thalamocortical, with the emergence of connective patterns. (Edelman; Remembered Present, 153)

Distribution of thalamocortical neurons may enhance the sensitivity of neurons in primary and sensory cortical areas. (Edelman; Remembered Present, 202)

Three main neuroanatomical motifs in the brain: (1) thalamocortical, (2) polysynaptic loop structure, (3) diffuse ascending projections of the different value systems. (Edelman; Wider than the Sky, 26)

Thalamocortical maps. (Edelman; Wider than the Sky, 53)

At a point in evolutionary time corresponding to the transition between reptiles and birds and between reptiles and mammals, a new reciprocal connectivity appeared in the thalamocortical system. (Edelman; Wider than the Sky, 54)

Dynamic reentrant interactions in the thalamocortical system. (Edelman; Wider than the Sky, 55)

Intralaminar nuclei, which send diffuse connections to most areas of the cortex, helped to synchronize thalamocortical responses and regulate the overall levels of activity in these multiple reentrant systems. (Edelman; Wider than the Sky, 55)

 

Thalamocortical system (Hobson; Dream Drugstore, 123)

Most neurocognitivists believe that the distributed and interconnected cortical circuits that are the physical substrate of conscious experience need to be synchronously activated, probably by the widely distributed thalamocortical system. (Hobson; Dream Drugstore, 176)

Most neurocognitivists believe that the source of activation of the thalamocortical system and the distributed forebrain circuits underlying consciousness is the brainstem reticular formation, and especially its pontine-mesencephalic and diencephalic components, which regulate the cortex via its interaction with the thalamocortical system. (Hobson; Dream Drugstore, 176)

Visual thalamocortical pathway, interaction with emotional pathways -  (illustration) (Johnston; Why We Feel, 114)

Thalamus and Cortex, thalamocortical connections (Koch; Quest for Consciousness, 124)

Llinás remarks on the thalamocortical system

Consciousness is a noncontinuous event determined by simultaneity of activity in the thalamocortical system. (Llinás; I of the Vortex, 124)

Thalamocortical activity as the functional basis for consciousness. (Baars; Essential Sources, Llinás & Paré, 965,)

Thalamic input from the cortex is far larger than from the peripheral sensory systems. This suggests that thalamocortical iterative activity is a main mechanism of brain function. (Llinás; I of the Vortex, 124)

The thalamocortical system, by its hublike organization, allows radial communication of the thalamic nuclei with all aspects of the cortex. These cortical regions include the sensory, motor, and associational areas. These areas subserve a feedforward/feedback, reverberating flow of information. (Llinás; I of the Vortex, 126)

What distinction is there between dreaming and wakefulness? If cognition is a function of the 40-Hz thalamocortical resonance, what happens to this oscillatory rhythm during sleep, particularly dream or REM sleep? (Llinás; I of the Vortex, 129)

40-Hz oscillations are not reset by sensory input during REM sleep, even though studies have clearly shown that the thalamocortical system is accessible to sensory input during sleep. (Llinás; I of the Vortex, 130)

Consciousness is a product of thalamocortical activity. (Llinás; I of the Vortex, 131)

FAPs are most probably implemented at the level of the basal ganglia and put into context by the reentry of the basal ganglia output into the ever-cycling thalamocortical system. (Llinás; I of the Vortex, 144)

Combine FAPs, emotions and consciousness into one directed output: Thalamocortical system, especially the non-specific intralaminar system, projects extremely aggressively to the basal ganglia. (Llinás; I of the Vortex, 169)

Working memory is the ability to hold the detail of significant content of the external world with the momentary internal context generated by the thalamocortical system. (Llinás; I of the Vortex, 182)

In the deep sleep state, sensory input of all types (modalities) is for the most part rejected by the thalamocortical system. (Llinás; I of the Vortex, 207)

 

Biogenic amine neurotransmitters function as neuromodulators that alter the membrane potential and firing patterns of thalamocortical and cortical neurons. (Purves; Neuroscience, 398)

Layer IV of the cortex gets most of its inputs from the thalamus. (Calvin; Neil’s Brain, 89)

 

 

Return to — Thalamocortical system