Tag Archives: Brain

Little Man Theater

Cartesian Theater

“Cartesian theater” is a derisive term coined by scientist Daniel Dennett to refer pointedly to a defining aspect of what he calls Cartesian materialism.

Descartes originally claimed that consciousness requires an immaterial soul, which interacts with the body via the pineal gland of the brain. Dennett says that, when the dualism is removed, what remains of Descartes’ original model amounts to imagining a tiny theater in the brain where a homunculus (small person), now physical, performs the task of observing all the sensory data projected on a screen at a particular instant, making the decisions and sending out commands (cf. the homunculus argument).

The term Cartesian Theater was brought up in the context of the multiple drafts model that Dennett posits in Consciousness Explained (1991):

Cartesian materialism is the view that there is a crucial finish line or boundary somewhere in the brain, marking a place where the order of arrival equals the order of “presentation” in experience because what happens there is what you are conscious of. Continue reading

Cortical Little Men

Homunculus
The homunculus is commonly used today in scientific disciplines such as psychology as a teaching or memory tool to describe the distorted scale model of a human drawn or sculpted to reflect the relative space human body parts occupy on the somatosensory cortex (the “sensory homunculus”) and the motor cortex (the “motor homunculus”). Both the motor and sensory homonculi usually appear as small men superimposed over the top of precentral or postcentral gyri for motor and sensory cortices respectively.

The homunculus is oriented with feet medial and shoulders lateral on top of both the precentral and the postcentral gyrus (for both motor and sensory). The man’s head is depicted upside down in relation to the rest of the body such that the forehead is closest to the shoulders. The lips, hands, feet and sex Continue reading

Temporal Lobe

Temporal Lobe

The temporal lobe is one of the four major lobes of the cerebral cortex in the brain. The temporal lobe is located beneath the lateral fissure on both cerebral hemispheres of the mammalian brain.

The temporal lobe is involved in processing sensory input into derived meanings for the appropriate retention of visual memories, language comprehension, and emotion association.

Medial temporal lobe

The medial temporal lobe consists of structures that are vital for declarative or long-term memory. Declarative (denotative) or explicit memory is conscious memory divided into semantic memory (facts) and episodic memory (events). Medial temporal lobe structures that are critical for long-term memory include the hippocampus, along with the surrounding hippocampal region consisting of the perirhinal, parahippocampal, and entorhinal neocortical regions. The hippocampus is critical for memory formation, and the surrounding medial temporal cortex is currently theorized to be critical for memory storage. The prefrontal and visual cortices are also involved in explicit memory. Continue reading

Longitudinal Fissure

Image result for cerebral hemispheresLongitudinal Fissure

fissure
1. a narrow slit or cleft, especially one of the deeper or more constant furrows separating the gyri of the brain.
2. in dermatology a deep crack in the skin, often through a scab, which penetrates into the subcutis.
3. a deep cleft in the surface of a tooth, usually due to imperfect fusion of the enamel of the adjoining dental lobes. It can be treated with a dental sealant to decrease risk of caries.

longitudinal fissure
Etymology: L, longitudo, length, fissura, cleft
the largest and deepest groove between the medial surfaces of the cerebral hemispheres.

longitudinal fissure
1. The fissure on the lower surface of the liver.
2. A fissure that separates the cerebral hemispheres. The corpus callosum, which connects the hemispheres, is at the base of the fissure. Continue reading

Science of Memory

Chapter 7: Learning and Memory
John H. Byrne, Ph.D.

7.1 Types of Memory

Psychologists and neuroscientists have divided memory systems into two broad categories, declarative and nondeclarative (Figure 7.1).

The declarative memory system is the system of memory that is perhaps the most familiar. It is the memory system that has a conscious component and it includes the memories of facts and events. A fact like ‘Paris is the capital of France’, or an event like a prior vacation to Paris.

Nondeclarative memory, also called implicit memory, includes the types of memory systems that do not have a conscious component but are nevertheless extremely important. They include the memories for skills and habits (e.g., riding a bicycle, driving a car, playing golf or tennis or a piano), a phenomenon called priming, simple forms of associative learning [e.g., classical conditioning (Pavlovian conditioning)], and finally simple forms of nonassociative learning such as habituation and sensitization. Sensitization will be discussed in detail later in the Chapter. Declarative memory is “knowing what” and nondeclarative memory is “knowing how”. Continue reading

Amygdala

Chapter 6: Limbic System: Amygdala
By Anthony Wright, Ph.D.

6.1 Amygdala – General Considerations

Amygdala is the integrative center for emotions, emotional behavior, and motivation. If the brain is turned upside down the end of the structure continuous with the hippocampus is called the uncus. If you peel away uncus you will expose the amygdala which abuts the anterior of the hippocampus. Just like with the hippocampus, major pathways communicate bidirectionally and contain both efferent and afferent fibers.

6.2 Inputs to the Amygdala

The amygdala receives inputs from all senses as well as visceral inputs. Since the amygdala is very Continue reading

Hippocampus

Chapter 5: Limbic System: Hippocampus
Anthony Wright, Ph.D.

5.1 Introduction to the Limbic System

Limbic is a Latin term which means border. Like the familiar word “limbo”, it means an intermediate or transitional state, which is a border. In this case, the border is between the neocortex and the subcortical structures (diencephalon). The limbic system includes the hippocampal formation, amygdala, septal nuclei, cingulate cortex, entorhinal cortex, perirhinal cortex, and parahippocampal cortex. These last three cortical areas comprise different portions of the temporal lobe. (Some experts would also include parts of the hypothalamus, thalamus, midbrain reticular formation, and olfactory areas in the limbic system.)

5.2 Hippocampus

The term hippocampal formation typically refers to the dentate gyrus, the hippocampus proper (i.e., Continue reading