what does this mean in area-4 of the brain Body representation: the body is topographically represented in an inverted (head-down) and crossed (opposite side) manner
This means that in area-4 of the brain, the representation of the body is organized in a specific pattern. The body is represented in a topographical manner, meaning that different parts of the body are mapped out in specific locations within this brain area. However, this representation is inverted, which means that the bottom part of the body is represented towards the top of the brain area, and the top part of the body is represented towards the bottom of the brain area. Additionally, the representation is crossed, which means that the left side of the body is represented towards the right side of this brain area, and vice versa. This arrangement of body representation in area-4 is often referred to as an "inverted and crossed" organization.
In area-4 of the brain, specifically in the primary motor cortex, the concept of body representation refers to how different body parts are mapped or represented within this region. The body is topographically represented means that the organization of body parts in the brain corresponds to the organization of body parts in the actual body. In other words, adjacent areas in the primary motor cortex represent adjacent body parts.
The phrase "inverted (head-down) and crossed (opposite side) manner" refers to the specific arrangement of the body representation within area-4. In this inverted manner, the representation of body parts in the brain is arranged upside-down compared to their actual position in the body. Meanwhile, the crossed arrangement means that the body parts on one side of the body are represented in the opposite hemisphere of the brain.
For example, the representation of the feet would be located at the top of the primary motor cortex, while the representation of the head would be found at the bottom. Similarly, motor commands for the right side of the body would be controlled by the left hemisphere of the brain, and vice versa.
In the area-4 of the brain, specifically in the primary motor cortex, there is a phenomenon known as "body representation." This refers to how the body is organized and mapped within this region of the brain. The concept of body representation in the primary motor cortex is often described using two fundamental characteristics: topographical representation and inverted/crossed representation.
1. Topographical Representation: Within the primary motor cortex, different body parts are represented in a specific and organized manner. This means that neighboring body parts are also represented in neighboring areas within the primary motor cortex. For example, the representation of the hand and fingers will be close to the representation of the wrist and forearm.
2. Inverted/Crossed Representation: The term "inverted" refers to the fact that the body representation in the primary motor cortex is upside-down, also known as head-down. This means that the top of your head is represented in the lower part of this brain area, while your feet and toes are represented in the upper part.
Additionally, the term "crossed" refers to the fact that the body representation in the primary motor cortex is also organized in a crossed or contralateral manner. This means that the left side of your body is represented in the right hemisphere of the primary motor cortex, and vice versa. So, when you move your right hand, the corresponding representation within the primary motor cortex is in the left hemisphere.
To understand this phenomenon, scientists have used methods such as electrical stimulation of specific brain areas to elicit movements or observing brain activity using functional imaging techniques like fMRI (functional Magnetic Resonance Imaging).
This inverted and crossed organization of body representation in the primary motor cortex is often referred to as the "homunculus" or the "motor homunculus." It visually represents this organized mapping of body parts within this brain region.