Lecture 29: Visual System 4: Ablations (cont.) (Orig: Electrophysiology)

TL;DR

Lesions in the visual cortex and superior colliculus in monkeys can affect visual perception and orienting movements. The colliculus plays a role in both visual processing and anti-predator behavior. Connections between the visual cortex and inferior temporal cortex are crucial for complex shape recognition.

Transcript

GERALD SCHNEIDER: This is class 31, which is listed on the syllabus for today's date. I'm sticking with the numbers on the syllabus-- we took one class out of order, the one Neville gave, that was class 29. OK, at the end of the last hour, we were talking about the Kluver-Bucy syndrome, due to large temporal lobe removals in monkeys. And I said tha... Read More

Key Insights

• ❓ The visual effects of lesions in different areas of the cortex depend on the specific regions affected and the connections disrupted.
• 🖐️ The inferior temporal cortex plays a crucial role in complex shape recognition, receiving visual inputs from multiple sources.
• 🫠 Disconnections between visual and speech mechanisms due to lesions or damage to the corpus callosum can lead to language and reading difficulties.
• 🧠 Regeneration and collateral sprouting of neurons can occur after early brain lesions, providing alternative connections in the brain.

Questions & Answers

Q: What are the visual effects of lesions in the inferior temporal neocortex?

Lesions in the inferior temporal neocortex lead to difficulties in perceiving and recognizing complex shapes and patterns. Visual impairments may arise, but scotomas (blind areas) are not typically observed.

Q: How does the inferior temporal cortex receive its visual inputs?

The inferior temporal cortex receives visual inputs through transcortical connections from the striate cortex, subcortical connections from the pulvinar nucleus of the thalamus, and input from the opposite side of the brain through the corpus callosum.

Q: What happens when lesions are made in the striate cortex and the inferior temporal cortex on opposite sides?

Lesions in the striate cortex on one side lead to a scotoma (blind area) in the corresponding half of the visual field. However, if additional lesions are made in the inferior temporal cortex on the opposite side, significant bilateral deficits similar to those observed in individuals with corpus callosum damage can occur, suggesting a disconnection between visual and speech mechanisms.

Q: Are there any specific response properties of neurons in the inferior temporal cortex?

Neurons in the inferior temporal cortex respond best to very complex shapes, such as monkey faces or hands. They exhibit receptive fields that include the fovea and have large receptive fields overall.

Summary & Key Takeaways

• Lesions in the inferior temporal neocortex can result in visual impairments, particularly in recognizing complex shapes and patterns.

• The inferior temporal cortex receives visual inputs from three main sources: transcortical input, subcortical input from the pulvinar nucleus of the thalamus, and input from the opposite side of the brain.

• Disconnecting the visual cortex from the inferior temporal cortex can lead to significant deficits in visual processing and affect language and speech abilities.