science

Perirhinal cortex

Perirhinal cortex is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Perirhinal cortex rather than just read about it. In short: The perirhinal cortex is a cortical region in the medial temporal lobe that is made up of Brodmann areas 35 and 36. It receives highly processed sensory information from all sensory regions, and is generally accepted to be an important region for memory.

Key takeaways

Perirhinal cortex belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Perirhinal cortex to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Perirhinal cortex from memory before moving on to harder problems.

Reference excerpt

The perirhinal cortex is a cortical region in the medial temporal lobe that is made up of Brodmann areas 35 and 36. It receives highly processed sensory information from all sensory regions, and is generally accepted to be an important region for memory. It is bordered caudally by postrhinal cortex or parahippocampal cortex (homologous regions in rodents and primates, respectively) and ventrally and medially by entorhinal cortex.

Structure The perirhinal cortex is composed of two regions: areas 36 and 35. Area 36 is sometimes divided into three subdivisions: 36d is the most rostral and dorsal, 36r ventral and caudal, and 36c the most caudal. Area 35 can be divided in the same manner, into 35d and 35v (for dorsal and ventral, respectively). Area 36 is six-layered, dysgranular, meaning that its layer IV is relatively sparse. Area 35 is agranular cortex (lacking any cells in layer IV).

Function The perirhinal cortex is involved in both visual perception and memory; it facilitates the recognition and identification of environmental stimuli. Lesions to the perirhinal cortex in both monkeys and rats lead to the impairment of visual recognition memory, disrupting stimulus-stimulus associations and object-recognition abilities. The perirhinal cortex is also involved in item memory, especially in coding familiarity or recency of items. Rats with a damaged perirhinal cortex seemed unable to tell novel objects from familiar ones—they were still more interested in exploring when novel objects were present, but examined the novel and familiar objects equally, unlike undamaged rats. Thus, other brain regions are capable of noticing unfamiliarity, but the perirhinal cortex is needed to associate the feeling with a specific source. The perirhinal cortex also receives a large dopaminergic input and signals the rewards that are associated with visual stimuli Damage to the perirhinal cortex has been shown to cause impairment in discriminating among object concepts when there is a high degree of visual semantic overlap among choices, such as between a hairdryer and a gun. A growing body of evidence suggests that the perirhinal cortex protects against interference from low-level visual features. The perirhinal cortex's role in the formation and retrieval of stimulus-stimulus associations (and in virtue of its unique anatomical position in the medial temporal lobe) suggest that it is part of a larger semantic system that is crucial for endowing objects with meaning.

Other animals

Primates The monkey perirhinal cortex receives a majority of its input from high-level visual areas, whereas, in the rat, its inputs are primarily olfactory and, to a lesser extent, auditory. Outputs to orbitofrontal cortex and medial prefrontal cortex regions (such as prelimbic and infralimbic) have been described. Perirhinal cortex also sends output to a number of subcortical structures, including the basal ganglia, the thalamus, the basal forebrain, and the amygdala. It also has direct connections with hippocampus region CA1 and the subiculum. Perirhinal cortex projects to distal CA1 pyramidal cells, overlapping the projections from entorhinal cortex. The same CA1 cells send return projections back to perirhinal cortex. Inputs from subiculum terminate in both superficial and deep layers. Visual areas TE and TEO send and receive a significant reciprocal connection with perirhinal cortex. Weaker, but still significant, projections come from other parahippocampal regions and from the superior temporal sulcus. Other inputs include anterior cingulate and insular regions, in addition to prefrontal projections.

Rodents Auditory inputs from temporal cortical regions are the primary inputs to rat 36d, with visual inputs becoming more prominent closer to the postrhinal cortical border. Area 36d projects to 36v and then to 35, which forms the primary output region of perirhinal cortex. Inputs to area 35 more strongly reflect olfactory and gustatory inputs from piriform and insular cortices, in addition to inputs from entorhinal cortex and frontal regions.

References

Witter MP and Wouterlood F. 2002. The parahippocampal region: organization and role in cognitive function. Oxford University Press: New York. Murray, E.A., & Bussey, T.J. (1999). Perceptual-mnemonic functions of the perirhinal cortex. Trends in Cognitive Sciences, 3(4), 142-151. Winters, B.D., Forwood, S.E., Cowell, R., Saksida, L.M., & Bussey, T.J. (2004). Double dissociation between the effects of peri-postrhinal cortex and hippocampal lesions on tests of object recognition and spatial memory: heterogeneity of function within the temporal lobe. Journal of Neuroscience, 24, 5901-5908.

Illustrations

Worked examples

Example 1 — a first encounter with Perirhinal cortex

Start with the simplest possible case. Write down what Perirhinal cortex claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Perirhinal cortex before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Perirhinal cortex ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Perirhinal cortex

In research: Perirhinal cortex appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Perirhinal cortex in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Perirhinal cortex is common in secondary-school and first-year university syllabi. It links to neighbouring topics Cerebral cortex, Limbic system, so understanding it makes those chapters shorter.
In everyday life: Look for Perirhinal cortex outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Perirhinal cortex in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Perirhinal cortex means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Perirhinal cortex out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Perirhinal cortex in simple terms?

Why does Perirhinal cortex matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Perirhinal cortex?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Perirhinal cortex.